BASE/2018    Open error (DISKSPACE() function)

     Default Behavior:  The program continues after returning an empty
     value.

     Explanation:  The disk does not exist or is not ready upon an
     attempt to access it with the DISKSPACE() function.

     Action:  Make sure to supply the correct drive number (for fixed
     disks) or call the DISKSPACE() function in a loop with a user warning
     when checking the readiness of a floppy drive.

     See Also:  COPY FILE command