Well i don't know if you have resolved the issue or not but the problem that you have described occurs if you have unwanted files in textsetup.oem.
The textmode portion of the setup only uses sys files and so when you use unattended installs you should not have any dll files etc in textsetup.oem.
Since the textsetup.oem is just the script that textmode portion of the setup reads so these files are not required. Especially the dll files. And these will give you an error that you are getting.
[Files.Scsi.hpn]
driver = d1, hpn.sys, hpn
catalog = d1, hpn.cat
inf = d1, hpn.inf
inf = d1, hpnmgt.inf
OMITT - dll = d1, hpncin.dll