SN: correction and explanation

The problem was solved rather quickly. Though the REPAIR query failed, dropping one index and recreating it was enough to make the table works normally again, it was just that specific index which was corrupted it seems.

Not is all well that ends well, I still haven't managed to fix the PM issue. However I found what is causing it and what may causing even more problems in the future: a compatibility bug with previous MySQL versions. MySQL authors claim it's not a bug, they just "conformed to the SQL 2003 Standard". It interpretes the precedence of operators differently during a join operation, and since I'm using an old version of IPB, from the time when they still offered free versions, it hasn't been optimized at all to support MySQL 5.

So if you get a "mySQL error: Unknown column 'm.id' in 'on clause'", you're most certainly having the same problem.