How do I diagnose a damaged data file?

A damaged data file displays the following symptoms:

Incorrect categories or numbers in reports even though all the report settings are correct
Missing dates in reports even though all the report settings are correct
Missing categories or tags
Inability to assign categories in split transactions
Inability to restore the backup of a Quicken data file
Inability to reconcile your current bank statement even though all the individual numbers are correct

You can take steps to repair your Quicken data file.