Problems with Cyrus and SquirrelMail

[Geoff Soper]

I've installed SquirrelMail (a PHP IMAP webmail client) on my webserver
and have it acessing my account on the mail server running Cyrus. Both are
commercially hosted and the hosting company doesn't support webmail
software. I have a problem with replying to messages, almost everytime I
go to send the reply I get:
ERROR : Connection dropped by imap-server.
Query: STORE 753:753 +FLAGS (\Answered)
By searching the source code and not finding this error I assume it comes
from Cyrus. I'm guessing it's having problems setting the answered flag on
the message that was replied to? Can anyone suggest why this might be the
case? Does anyone have any experience of SquirrelMail and Cyrus? What can
I do next in the way of diagnosis or remedy?

Thanks in advance!
Geoff