Same issue for me, connection seems to drop usually in the early hours only a reboot restores it. Actually just dropped a few minutes ago.
Thu Mar 25 16:19:07 2010 Critical (3) No Ranging Response received - T3 time-out
Thu Mar 25 16:19:09 2010 Critical (3) Ranging Request Retries exausted
Thu Mar 25 16:19:09 2010 Critical (3) Unicast Maintenance Ranging attempted - No response - Retries exhausted
Connection Drops! sync lights goes out and then blinks for a few seconds then stays on solid but have to reboot the modem to get the net back on. I had this issue most nights earlier in the year and I thought it was now resolved but in the last week I'm seeing this quite often again. It drops even when I'm hard wired directly to the CM. Newsgroups have been no help, they tell me to call them when it disconnects, but their closed
I do try to be a good boy and leave my downloads running overnight but I'm reluctant to do this if the connection is going to drop out.
The frequency of the disconnections I'm seeing make me think it is unlikely due to maintenance work and I'm told my uBR has already been patched. Not sure if it's relevant but about the time I started seeing this issue again coincides with when the upstream mini-slot changed from 2 to 4.