Dave,

Do you have syslog enabled? I found that with rc5b I had syslog enabled but not set to record to anything (ie not to syslog or usb) and it wasn't happy. After setting the to syslog check box it was ok again.

What symptoms did you experience with the router before you made this change ?

I had issues for months with the Dial plan / Digit map broken, chopping out numbers etc, with this new code it is fixed. I had a ticket open.
Seems to be stable for me on a 2820Vn, but do not use the 'n', up time is just 35 hours though...See how it goes.