ProDOS Error Codes 

hex code                Meaning
-------       --------------------------------
  00          No error
  01          Invalid number for system call
  04          Invalid param count for system call
  25          Interrupt vector table full
  27          I/O Error
  28          No device connected/detected
  2b          Disk write protected
  2e          Disk switched
  40          Invalid characters in pathname
  42          File control block table full
  43          Invalid reference number
  44          Directory not found
  45          Volume not found
  46          File not found
  47          Duplicate file name
  48          Volume Full
  49          Volume directory full
  4a          Incompatible file format
  4b          Unsupported storage type
  4c          End of file encountered
  4d          Position out of range
  4e          File Access error; eg, file locked
  50          File is open
  51          Directory structure damaged
  52          Not a ProDOS disk
  53          Invalid system call parameter
  55          Volume control block table full
  56          Bad buffer address
  57          Duplicate volume
  5a          Invalid address in bit map