B.1 BASIC Run-Time Errors by Mnemonic
  The BASIC error message format is as follows:
  %BAS-<l>-<mnemonic>, <message> -BAS-I-FROLINMOD, from Line x
  in module y

  <l>
  Is a letter indicating the severity of the error. The severity
  indicator can be one of the following:

  .
        I-Indicating information
  .
        W-Indicating a warning
  .
        E-Indicating an error
  .
        F-Indicating a severe error

  <mnemonic>
  Is a 3- to 9-character string that identifies the error.

  <X>
  Is the line number where the error occurred.

  <Y>
  Is the name of the module where the error occurred.

  Warning error messages indicate that an error has occurred,
  but program execution continues. In some cases, BASIC
  reprompts 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.