On return, register 15 will contain a return code. If the invocation
fails, it may be for one of the following reasons:
- If you request a function that is not valid or a combination of
functions that are not valid, register 15 contains a return code of
28 and the request fails.
- If the JES control table (JESCT) does not contain valid pointers,
the environment is incorrect. Register 15 contains a return code
of 24. The request fails.
- If an empty UCB list is being returned to the caller, register
15 contains a return code of 36.