Unfortunately, disabling multi-link and LCP didn't make any difference
Here's an extract from the modem log showing what happened. The first time I try to connect it seems to work, but only connect at 28.8k - nothing happens after that. When I disconnect and then try to reconnect, it will stall at the "authenticating password" stage.
02-20-2001 23:55:30.850 - Modem type: U.S. Robotics 56K Voice Win
Int
02-20-2001 23:55:30.850 - Modem inf path: mdm00c4.inf
02-20-2001 23:55:30.850 - Modem inf section: Modem1807_2K
02-20-2001 23:55:30.881 - Opening Modem
02-20-2001 23:55:30.881 - 115200,8,N,1, ctsfl=1, rtsctl=2
02-20-2001 23:55:30.881 - Initializing modem.
02-20-2001 23:55:30.891 - Send: AT<cr>
02-20-2001 23:55:30.901 - Recv: AT<cr>
02-20-2001 23:55:30.901 - Command Echo
02-20-2001 23:55:30.901 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:55:30.901 - Interpreted response: OK
02-20-2001 23:55:30.911 - Send: AT&F&A0&B1&C1&D2E0Q0V1S0=0<cr>
02-20-2001 23:55:30.921 - Recv: AT&F&A0&B1&C1&D2E0Q0V1S0=0<cr>
02-20-2001 23:55:30.921 - Command Echo
02-20-2001 23:55:30.921 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:55:30.921 - Interpreted response: OK
02-20-2001 23:55:30.941 - Send: AT+ILRR=1;+MR=1;+ER=1;+DR=1<cr>
02-20-2001 23:55:30.951 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:55:30.951 - Interpreted response: OK
02-20-2001 23:55:30.961 - Send:
ATS7=60S19=0L2M1+ES=3,0,2;+DS=3,0;<cr>
02-20-2001 23:55:30.971 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:55:30.971 - Interpreted response: OK
02-20-2001 23:55:30.981 - TSP(0000): Making call
02-20-2001 23:55:30.981 - Send: AT+IFC=2,2;B0X4<cr>
02-20-2001 23:55:30.981 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:55:30.981 - Interpreted response: OK
02-20-2001 23:55:30.981 - Waiting for a call.
02-20-2001 23:55:30.991 - Send: ATS0=0<cr>
02-20-2001 23:55:31.021 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:55:31.021 - Interpreted response: OK
02-20-2001 23:55:31.021 - 115200,8,N,1, ctsfl=1, rtsctl=2
02-20-2001 23:55:31.021 - Initializing modem.
02-20-2001 23:55:31.031 - Send: AT<cr>
02-20-2001 23:55:31.031 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:55:31.031 - Interpreted response: OK
02-20-2001 23:55:31.061 - Send: AT&F&A0&B1&C1&D2E0Q0V1S0=0<cr>
02-20-2001 23:55:31.071 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:55:31.071 - Interpreted response: OK
02-20-2001 23:55:31.081 - Send: AT+ILRR=1;+MR=1;+ER=1;+DR=1<cr>
02-20-2001 23:55:31.131 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:55:31.131 - Interpreted response: OK
02-20-2001 23:55:31.141 - Send:
ATS7=60S19=0L2M1+ES=3,0,2;+DS=3,0;<cr>
02-20-2001 23:55:31.151 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:55:31.151 - Interpreted response: OK
02-20-2001 23:55:31.161 - Send: AT+IFC=2,2;B0X4<cr>
02-20-2001 23:55:31.161 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:55:31.161 - Interpreted response: OK
02-20-2001 23:55:31.161 - Dialing.
02-20-2001 23:55:31.161 - TSP(0000): LINEEVENT:
LINECALLSTATE_DIALING
02-20-2001 23:55:31.161 - TSP(0000): LINEEVENT:
LINECALLSTATE_PROCEEDING
02-20-2001 23:55:31.171 - Send: ATDT####,###########<cr>
02-20-2001 23:56:03.527 - Recv: <cr><lf>+MCR: V90<cr><lf>
02-20-2001 23:56:03.527 - Interpreted response: Informative
02-20-2001 23:56:03.527 - Recv: <cr><lf>+MRR: 28800<cr><lf>
02-20-2001 23:56:03.527 - Interpreted response: Informative
02-20-2001 23:56:03.527 - Recv: <cr><lf>+ER: MNP<cr><lf><cr><lf>+DR:
MNP5<cr><lf><cr><lf>
02-20-2001 23:56:03.527 - An unknown response was received while
attemping to connect, but CD was high so completeing successfully
02-20-2001 23:56:03.527 - Connection established at 28800bps.
02-20-2001 23:56:03.527 - Error-control off or unknown.
02-20-2001 23:56:03.527 - Data compression off or unknown.
02-20-2001 23:56:03.527 - TSP(0000): LINEEVENT:
LINECALLSTATE_CONNECTED
02-20-2001 23:56:33.531 - Read: Total: 0, Per/Sec: 0, Written:
Total: 0, Per/Sec: 0
02-20-2001 23:58:21.736 - CD dropped--Remote modem hung up.
ModemStatus=00000038
02-20-2001 23:58:21.736 - TSP(0000): LINEEVENT:
LINECALLSTATE_DISCONNECTED(0x1)
02-20-2001 23:58:21.736 - TSP(0000): Dropping call
02-20-2001 23:58:21.736 - Hanging up the modem.
02-20-2001 23:58:22.367 - Recv: <cr><lf>NO CARRIER<cr><lf>
02-20-2001 23:58:22.367 - Interpreted response: No Carrier
02-20-2001 23:58:22.377 - Send: ATH<cr>
02-20-2001 23:58:22.708 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:58:22.708 - Interpreted response: OK
02-20-2001 23:58:22.718 - Send: at#ud<cr>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263 0=10><cr><lf>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263 1=7 2=0 3=0><cr><lf>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263
4="E0C1651390478D"><cr><lf>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263 5=><cr><lf>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263 10=14><cr><lf>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263 11=F><cr><lf>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263 12=3202><cr><lf>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263 13=0><cr><lf>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263 14=E><cr><lf>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263 15=0><cr><lf>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263 16=E><cr><lf>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263 17=E><cr><lf>
02-20-2001 23:58:22.728 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.728 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.728 - Recv: <2A4D3263 20=C 21=E><cr><lf>
02-20-2001 23:58:22.788 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.788 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.788 - Recv: <2A4D3263 22=C80><cr><lf>
02-20-2001 23:58:22.788 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.788 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.788 - Recv: <2A4D3263 23=1F40><cr><lf>
02-20-2001 23:58:22.848 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.848 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.848 - Recv: <2A4D3263 24=780><cr><lf>
02-20-2001 23:58:22.848 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.848 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.848 - Recv: <2A4D3263 25=780><cr><lf>
02-20-2001 23:58:22.848 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.848 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.848 - Recv: <2A4D3263 26=7080 27=C5EA><cr><lf>
02-20-2001 23:58:22.848 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.848 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.848 - Recv: <2A4D3263 30=0><cr><lf>
02-20-2001 23:58:22.848 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.848 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.848 - Recv: <2A4D3263 31=0><cr><lf>
02-20-2001 23:58:22.848 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.848 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.848 - Recv: <2A4D3263 32=0 33=0><cr><lf>
02-20-2001 23:58:22.848 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.848 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.848 - Recv: <2A4D3263 34=7080 35=C5EA><cr><lf>
02-20-2001 23:58:22.848 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.858 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.858 - Recv: <2A4D3263 40=2><cr><lf>
02-20-2001 23:58:22.858 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.858 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.858 - Recv: <2A4D3263 41=80 42=0 43=0
44=80><cr><lf>
02-20-2001 23:58:22.858 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.858 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.858 - Recv: <2A4D3263 50=2 51=2><cr><lf>
02-20-2001 23:58:22.858 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.858 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.858 - Recv: <2A4D3263 52=509 53=38B 54=0
55=0><cr><lf>
02-20-2001 23:58:22.858 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.858 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.858 - Recv: <2A4D3263 56=49 57=3E 58=0
59=0><cr><lf>
02-20-2001 23:58:22.858 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.858 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.858 - Recv: <2A4D3263 60=51><cr><lf>
02-20-2001 23:58:22.858 - Recv: <cr><lf>DIAG
02-20-2001 23:58:22.858 - Interpreted response: Diagnostic Info
02-20-2001 23:58:22.858 - Recv: <2A4D3263
FF=3COM-USROBOTICS><cr><lf>
02-20-2001 23:58:22.858 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:58:22.858 - Interpreted response: OK
02-20-2001 23:58:22.858 - Diagnostics
02-20-2001 23:58:22.858 - Modem Diagnostics:
02-20-2001 23:58:22.858 - Version 1.0
02-20-2001 23:58:22.858 - Call Setup Result: Data Answering signal
detected
02-20-2001 23:58:22.858 - Multi-media mode: Data Only
02-20-2001 23:58:22.858 - DTE-DCE interface mode: Async data
02-20-2001 23:58:22.858 - V.8 CM octet string: "E0C1651390478D"
02-20-2001 23:58:22.858 - Received signal power level (in -dBm): 20
02-20-2001 23:58:22.858 - Transmit signal power level (in -dBm): 15
02-20-2001 23:58:22.858 - Estimated noise level (in -dBm): 12802
02-20-2001 23:58:22.858 - Normalized Mean Squared error: 0
02-20-2001 23:58:22.858 - Near echo loss: 14 dB
02-20-2001 23:58:22.858 - Far echo loss: 0 dB
02-20-2001 23:58:22.858 - Far echo delay: 14 ms
02-20-2001 23:58:22.858 - Round Trip delay: 14 ms
02-20-2001 23:58:22.928 - Transmit Carrier Negotiation Result: V.34
02-20-2001 23:58:22.928 - Receive Carrier Negotiation Result: V.pcm
(asymmetric)
02-20-2001 23:58:22.928 - Transmit Carrier symbol rate: 3200
02-20-2001 23:58:22.928 - Receive Carrier symbol rate: 8000
02-20-2001 23:58:22.928 - Transmit Carrier frequency: 1920
02-20-2001 23:58:22.928 - Receive Carrier frequency: 1920
02-20-2001 23:58:22.928 - Initial transmit carrier data rate: 28800
02-20-2001 23:58:22.928 - Initial receive carrier data rate: 50666
02-20-2001 23:58:22.928 - Temporary carrier loss event count: 0
02-20-2001 23:58:22.928 - Carrier Rate re-negotiation event count: 0
02-20-2001 23:58:22.928 - Carrier Retrains requested: 0
02-20-2001 23:58:22.928 - Carrier Retrain requests granted: 0
02-20-2001 23:58:22.928 - Final transmit carrier rate: 28800
02-20-2001 23:58:22.928 - Final receive carrier rate: 50666
02-20-2001 23:58:22.928 - Protocol Negotiation Result: V.42
Alterative protocol (MNP)
02-20-2001 23:58:22.928 - Error control frame size: 128
02-20-2001 23:58:22.928 - Error control link timeouts: 0
02-20-2001 23:58:22.928 - Error control link NAKs: 0
02-20-2001 23:58:22.928 - Compression Negotiation Result: MNP5
02-20-2001 23:58:22.928 - Transmit flow control: V.24 ckt 106/133
02-20-2001 23:58:22.928 - Receive flow control: V.24 ckt 106/133
02-20-2001 23:58:22.928 - Transmit characters sent from DTE: 1289
02-20-2001 23:58:22.928 - Received characters sent to DTE: 907
02-20-2001 23:58:22.928 - Transmit characters lost (data overrun
errors from DTE): 0
02-20-2001 23:58:22.928 - Received characters lost (data overrun
errors to DTE): 0
02-20-2001 23:58:22.928 - Transmit Frame count: 73
02-20-2001 23:58:22.928 - Received Frame count: 62
02-20-2001 23:58:22.928 - Transmit Frame error count: 0
02-20-2001 23:58:22.928 - Received Frame error count: 0
02-20-2001 23:58:22.928 - Termination Cause: DTE Hangup Command
02-20-2001 23:58:22.928 - 115200,8,N,1, ctsfl=1, rtsctl=2
02-20-2001 23:58:22.938 - Initializing modem.
02-20-2001 23:58:22.948 - Send: AT<cr>
02-20-2001 23:58:22.958 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:58:22.958 - Interpreted response: OK
02-20-2001 23:58:22.968 - Send: AT&F&A0&B1&C1&D2E0Q0V1S0=0<cr>
02-20-2001 23:58:22.978 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:58:22.978 - Interpreted response: OK
02-20-2001 23:58:22.988 - Send: AT+ILRR=1;+MR=1;+ER=1;+DR=1<cr>
02-20-2001 23:58:22.998 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:58:22.998 - Interpreted response: OK
02-20-2001 23:58:23.008 - Send:
ATS7=60S19=0L2M1+ES=3,0,2;+DS=3,0;<cr>
02-20-2001 23:58:23.008 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:58:23.008 - Interpreted response: OK
02-20-2001 23:58:23.018 - Send: AT+IFC=2,2;B0X4<cr>
02-20-2001 23:58:23.028 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:58:23.028 - Interpreted response: OK
02-20-2001 23:58:23.028 - Waiting for a call.
02-20-2001 23:58:23.038 - Send: ATS0=0<cr>
02-20-2001 23:58:23.038 - Recv: <cr><lf>OK<cr><lf>
02-20-2001 23:58:23.038 - Interpreted response: OK
02-20-2001 23:58:23.038 - TSP(0000): LINEEVENT: LINECALLSTATE_IDLE
02-20-2001 23:58:23.048 - TSP(0000): Closing Call
02-20-2001 23:58:23.058 - Session Statistics:
02-20-2001 23:58:23.058 - Reads : 0 bytes
02-20-2001 23:58:23.058 - Writes: 0 bytes