I'm having the same problem since upgrading to 1.5.8
Any ideas anyone as this is causing me real problems?
I also can't downgrade to an older version without getting a load of errors
EDIT
OK scrap that I think I found the fix.
https://vborg.vbsupport.ru/showthread.php?t=120624
(the first "table_prefix" part was already fixed, the removal of the ' wasn't
Thanks Geek