If you have your profile in a shared folder on a network drive and launch Thunderbird immediately after starting your PC, you may need to open Explorer to make a connection to the shared folder before you launch Thunderbird.
So, if you see this error, close the Thunderbird error message, open Explorer and navigate to the drive which contains the shared folder, then try launching Thunderbird again. This works for me. It seems that Thunderbird can't start the first connection to a shared folder on a network drive.
Tim Winch
November 2007