     Error Message #73:  DOS MISMATCH (73, CBM DOS V2.6 1541)

      DOS 1 and 2 are read compatible but not write compatible. Disks may be
      interchangeably read with either DOS, but a disk formatted on one version
      cannot be written upon with the other version because the format is
      different. This error is displayed whenever an attempt is made to write
      upon a disk which has been formatted in a non-compatible format. (A utility
      routine is available to assist in converting from one format to another.)
      This message may also appear after power up.