exact same problem (couldnt access ezboard, with BEFW11S4 - Wireless-B Broadband Router - Version 4) al of a sudden. The firmware would work for a couple of months, then the problem would appear (where i wouldnt be able to see ezboard now).
I sent an email to linksys, and they told me to enable the mtu set the MTU to 1300 in the router setup and that had fixed my problem (I can now access ezboard ).
Hope that fixes your problem,
RKS