Repair and Fragmentation
  Errors.
    Lost cluster - marked in use, but no path to it.
  
    Cross-linked clusters - more than one file claims it.

    Invalid Directory entries - no parent directory, invalid start cluster,
      invalid date or time.

    Fragmentation (not error, just problem).  

  Utilities for repairing the FAT. Scandisk, Norton Utilities.
    Compare the two FATs.

    Check correct directory entries.

    Check the file chains.

    Check correct listing of available clusters.

  Clusters of a file may be distributed randomly across a partition.
    Defragmentation rearranges clusters to be optimally positioned.