Cheers for the pm
When you upgrade from 1.7 to 1.8 you are required to run two additional SQL files comments fix and structurefix
What you need to do is restore back to the 1.7.5 database backup you made before you upgraded.
Run the 1.7to1.8.sql, then the commentsfix.sql then the structurefix.sql then the 1.7to1.8.sql again for good measure
Now run the 1.8to1.9.sql and if you have it the 1.9to.1.9.2.sql
Do not run commentsfix or structurefix more than once or at any other stage as data lost and corruption will occur.