sounds like what i see on linux in bug 51330, except the errors also appears when folders or mails are selected.
First of all, I assume you mean "account in folderpane" with "mail server (not a folder)". Since you can't click any of those buttons you mention, this bug should be INVALID. It is unreproducable and no longer a bug. Marking INVALID.
verifying bugs... build 2001013020