Errors that occur during execution of your program are reported by
  diagnostic messages from the Run-Time Library.  These messages can
  result from hardware conditions, file system errors, errors
  detected by RMS, errors that occur during transfer of data
  between the program and an internal record, computations that cause
  overflow or underflow, incorrect calls to the Run-Time Library,
  problems in array descriptions, and conditions detected by the
  operating system.

  This section lists the run-time diagnostic messages without the
  prefixes FOR, SS, and MTH.  For each mnemonic, the following
  information is provided:  the message number, an error code (F for
  fatal, E for error, and I for information), the message text, and
  an explanation of the message.