imap no longer checking for messages

[seph]

Hi, my gnus is behaving rather oddly, and I'm not sure how to debug or
fix it.

I'm running "No Gnus v0.6" on a debian machine, primarily as an imap
client. My imap server is configured in gnus-secondary-select-methods. 
I've got a couple hundred groups on it, and it generally works fine.

Yesterday, something caused my emacs to crash. Since then, gnus
doesn't check for new messages in all the groups when I press "g". 
Interestingly, it does check groups with the (nnimap "foo") method,
but not groups with "nnimap:foo" method. This is unfortunate.

I tried resubscribing to some groups. The newly subscribed groups get
the (nnimap "foo") method, which works. But after changing it back to
"nnimap:foo" they stop being checked.

Grasping at straws, and searching the internet, I tried clearing out
the ~/News/ directory, it didn't help. I looked at imap-log, but I
don't see anything apart from the Updating commands. 

Any suggestions?

thanks
seph