B. Run-Time Error Messages
  BASIC returns run-time error messages if an error oc-
  curs while a program is executing. The error is diagnosed
  and for programs without line numbers, BASIC indicates
  the program line that generated the error. Warning error
  messages indicate that an error has occurred, but program
  execution continues. In some cases, BASIC prompts again
  for more information or correct data; in other cases, BASIC
  performs the specified operation, but the results are not as
  expected. Fatal error messages indicate that the program has
  aborted. You can recover from most fatal errors by including
  error-handling routines in your program and by specifying
  OPTION HANDLE = SEVERE. Certain errors, however, are
  not recoverable even when error-handlers are used. In the
  description of these errors, they are designated as not trap-
  pable. You do not need error-handling routines to trap errors
  that generate warning messages.

  Section B.1 lists BASIC run-time errors, alphabetized by
  mnemonic code. Section B.2 is a cross-reference numerical
  listing of run-time errors generated by BASIC. Section B.3
  lists error messages that BASIC does not generate, but which
  can be displayed with the ERT$ function. See the DEC BASIC
  and VAX BASIC for OpenVMS Systems Reference Manual
  for information about RMSSTATUS and VMSSTATUS.