CSCsk43903 -A pair of CSMs configured for fault tolerant operation will both enter the active state after 828 days, causing VIPs to be inaccessible. Fixed in 4.2(7).
I came across this bug which thankfully happened on a Sunday!
It's not clear wether the CSM requires rebooting to work around this bug before the 828 days expire or the switch chassis. Certainly the sh ver output from the switch showed exactly 828 days when I came across this problem.
I gather it's the CSM that requires rebooting, just want to be certain, anyone know? I have another pair of CSM's that come up to the 828 day limit(I'm not upgrading the code as yet, these CSM's will be replaced shortly)