I had run TMSXTEND to test the extended TMC, but even after I reverted back to a non-extended TMC, by restoring the TMC/Audit, I receive an S0C7 Abend during TMSINIT.
CA 1 rel 12.6 and above.
CA 1 has been activated with a TMC in the new enhanced format and they are now trying to restore back to the old format.
If you convert to an extended TMC for the first time and want to go back to an old-format TMC, you will always have to IPL all systems that were converted.
This is because information required for the handling of the new format is stored in the TMVT whenever an extended TMC is activated by TMSINIT or dynamically by TMSMRINT (invoked during the TMSXTEND process).
This TMVT update cannot be reverted. When CA-1 is then restarted pointing to an old-format TMC, the extraneous information is not reset and causes S0C4 or S0C7 abends.
If you know you want to backout after a test extend, you can limit the systems involved by specifying EXCLUDE statements in the CPULIST DD. However, you need to make sure that no tape processing occurs on the excluded systems sharing the TMC, and that TMSINIT is run after the backout and rename of the original TMC. The exclusion can help to reduce the number of IPLs required. Refer to the CA-1 Tape Management Utilities and Report Reference Guide for full details.