A Huge Dilemma

I play Sudoku on websudoku.com, and I absolutely despise when I click on "How am I doing?", and it responds "Something's not right in one of the cells".  If I ask "How am I doing?", and I have a mistake, obviously I have no idea where I made the mistake.  I try not to make any mistakes.  Just highlight the mistakes, and I'll delete them.