IMP 2.2.6 broken - users logged out when they click any link

[Matt Jeppsen]

Lately I've been lurking, just learning from all the list traffic.
Well, now I'm in need of a little help.

We've been running IMP 2.2.6 on a RH7.1 box with no problems for about 3
months now. Love it!

After the last power outage (I was 250 miles away when it happened, of
course), IMP allows users to login, but when they try to click any of the
buttons/links, they are logged out and presented with the login page again.

Clicking on: "Folders", "Preferences", ANY message, the folder "Refresh"
button, etc will log any user out.
Clicking on: "Compose", or "Contacts" just displays a blank page.

All I can guess is that the browser somehow isn't getting passed the auth
cookie, but it is purely speculation.
I can think of NOTHING that I've done to the server in the last few days
that may have caused this...
Where do I start in tracking down what I (apparently) broke?
Thanks!
-Matt