For BBj-specific information, see !ERROR Changes in BBj.
PRO/5 issues !ERROR=13 when an attempt is made to perform an operation on a file that is not meaningful for that type of file. For example, loading a non-program file into memory as resident, or dropping a peripheral device or nonresident program gives an !ERROR=13. !ERROR=13 may also occur if the file is not in the necessary state (i.e. does not have correct operating system permissions).
Attempting to perform a READ from a write-only device, such as a printer.
Attempting to perform a WRITE or PRINT to a read-only device.
Attempting to perform output during input via an IOLIST on a channel OPENed to a file other than a terminal.
Attempting to perform a WRITE to a SERIAL file before locking the file.
Attempting to open files on a Windows NT machine from a Windows 95 machine without the appropriate permissions at the OS level.
Attempting to access keys in a non-keyed file.
Attempting to perform a READ RECORD from a byte-oriented file without the SIZ= option.
Attempting to perform a DROP on a program that was not loaded into memory as resident.
Attempting to perform a READ from an MKEYED file with IND= clause.
Attempting to perform a WRITE to an MKEYED file with IND= clause.
Attempting to perform a WRITE to a single-key MKEYED file with KNUM= clause.
Attempting to perform a WRITE to a multi-key MKEYED file with KEY= clause.
Attempting to perform a KEY() function with MKEYED file with IND= clause.
Attempting to perform an INPUT on a keyed file read on a stream-oriented device such as a terminal, serial port, or string file when a DIR= clause is used.