I too got the (now notorious) "Time Machine Error - Unable to complete backup" error message. But happily, I got it fixed. I don't know which of the following steps did the trick, but so far the Time Machine (TM) seems to working. (NB. I haven't tried restoring the backup.)
System: Mac Mini (internal HD is [...]
A pastor of our international church in Espoo said that SquirrelMail wasn't working anymore. The frame where the folders used to be, now said
ERROR:
ERROR: Could not complete request.
Query: CREATE "Sent Messages"
Reason Given: Invalid mailbox name.
The fix involves two easy steps, the latter being voluntary.
Rename .sqmaildata folder (in your file system root) to something else, say, [...]