David Townsend writes:

There's no such thing as an "0x800CCC0f" error in IMAP. This is an error code returned by whatever IMAP client you are using, which is probably Outlook Express, which has a tendency to assume that whoever using it is a bloody moron who is too stupid to understand the real error message that's returned by the IMAP server, so instead of reporting the real error message, it gets replaced by a randomly generated number that Outlook Express believes, for some reason, is more meaningful than the original error message.

Check Microsoft's documentation to obtain an explanation of what this mythical error actually means. Then, when you know what it's actually complaining about you'll be in a better position to know where to look. But until the real error condition is known, you'll just have to roll the dice and bet that someone who has nothing to do on a weekend, except to read this mailing list, happens to remember what that specific error code means in Microsoft's universe.