| Code | ProDOS message | Most common cause |
| 2 | RANGE ERROR | Command option too small or large |
| 3 | NO DEVICE CONNECTED | Command option too small or large |
| 4 | WRITE PROTECTED | Write-protect tab on disk |
| 5 | END OF DATA | Read beyond end of file or record |
| 6 | PATH NOT FOUND | No file with indicated pathname |
| 7 | PATH NOT FOUND | No file with indicated pathname |
| 8 | I/O ERROR | Door open or disk not formatted |
| 9 | DISK FULL | Too many files on a disk |
| 10 | FILE LOCKED | Attempt to write to a locked file |
| 11 | INVALID OPTION | Option inappropriate for command |
| 12 | NO BUFFERS AVAILABLE | Memory full; file can't be opened |
| 13 | FILE TYPE MISMATCH | Disk file wrong type for command |
| 14 | PROGRAM TOO LARGE | Apple II's memory too small (CHAIN) |
| 15 | NOT DIRECT COMMAND | Comand must be in a program |
| 16 | SYNTAX ERROR | Bad filename, option, or comma |
| 17 | DIRECTORY FULL | Volume directory has 51 files |
| 18 | FILE NOT OPEN | Attempt to open a closed file |
| 19 | DUPLICATE FILENAME | RENAME, CREATE name already used |
| 20 | FILE BUSY | File already open |
| 21 | FILE(S) STILL OPEN | Last program didn't close file(s) |