If the recovery routine was entered due to system completion code 05C, register 0 contains a reason code. See z/OS MVS System Codes for an explanation of system code 05C and reason codes. If the recovery routine was entered due to an error related to allocation address space processing, message IEF100I is also issued. See z/OS MVS System Messages, Vol 8 (IEF-IGD) for an explanation of message IEF100I.