1757-SRM Firmware Update

Good day.

Bit of an unusual problem. I have a simple rack composed of a 1756-L63, a 1757-SRM and a 1756-ENBT (Yes, all old and pretty much not supported). Obviously I have a second rack comprised of the same modules.

Objective of the two racks is to test upgrading L63 from v16 to v20. Test successful. Both racks synchronized and failed over correctly. Not the point of this post.

Looking at the ENBT firmware, I upgraded both to 6.001. Also successful.

Looking at the SRM firmware, I tried to upgrade both to 5.001. This is where the problem is. I upgraded the secondary SRM to 5.001. Successful and synced. Great. I upgrade the primary SRM to 5.001. Firmware installation successful. Sync failed. The display shows "PRIM !CPT". The best I can find for help documentation related to "!CPT" is for v16 firmware (which I included as an attachment). Is the problem with standard vs enhanced? How can I tell?

I revert the primary SRM back to 4.004 and instantly the racks are synced. I am scratching my head how they can sync with different firmware installed. I pulled both SRMs and switched rack location. Again, the SRM 5.001 failed with !cpt. Revert the firmware to 4.004 and everything is fine.

Any suggestions are welcome.

I have since reverted both SRMs to 4.004 and they are both synced and happily blinking green lights. I also have a quote out for 1756-RM2.

Further update:
The other day one of my 1757-SRM modules failed (live system, not test bench). On a delay, I pulled the module and installed one of few spares. Since I had the time, I upgraded the firmware to 5.001. Module came online and synced. No issues. I upgrade the other 1757-SRM to 5.001. Firmware upgrade successful. Sync failed with "PRIM !CPT". I revert the module to 4.004. Firmware successful. Sync successful.

Scratching my head here. Oh well. System online.