Honeywell HPM Redundancy Failed. The "Alternate Path" doesn't work either?

Hi. I am really stumped with this one ....

After many years of operation and no recorded "event" an HPM redundancy failed. The backup HPM cards were replaced but the backup HPM always fails during the LOADING, SYNC steps. Based on the primary HPM diagnostics it has been determined the problem is not with the backup HPM, the problem resides in the primary HPM. To replace the primary (now non-redundant) HPM cards require a plant shutdown.

My past trouble shooting/repair efforts are as follows:

1. As per Honeywell recommendation, I have tried loading the failed backup HPM via the "Alternate Path" multiple times, with and without a new Redundancy Cable every time without success.

2. Suspecting a corrupt system file I have copied and used new personality image files then tried loading the HPM again without success.

3. During a plant shutdown both HPM's were replaced but still there is no redundancy. As usual when the backup HPM is being loaded its status goes from LOADING to SYNC to FAIL. .... The databases still will not synchronize ....

4. Currently plans are being made to replace everything; card files, I/O Link cables, etc. at the next plant shutdown in a couple of years.

I would like to know if anyone else has similar experience and what they did to fix the issue? Also I would be happy to entertain any/all suggestions.

Thank you in advance.