Single bit warning error rate exceeded

I haven't used the Server Administrator version you specified, but I do use the firmware versions you specified on many PE6400's and PE6450's.  Since you have already replaced the DIMM in Bank_1/DIMM_A and the Memory Riser card, please consider shutting down the server and temporarily removing the Memory Riser Card.  Use a flashlight to examine the pins on the motherboard that plug into the Memory Riser Card.  If you see one bent, definitely replace the motherboard and confirm that the Memory Riser Card connector is straight.  If I remember correctly the Memory Riser Card connector is two (or more) connectors bonded together (at one point I think there was a metal band, but now I believe it is only glue on the newer 'revisions').

 

Even if you don't see bent pins it may be worthwhile to replace the motherboard because I don't think that you are seeing a firmware related issue if you are seeing memory errors in the ESM/Hardware Log in Server Administrator.

 

Please keep in mind that the guide (or lack thereof) for the Memory Riser card into the motherboard on the PE6400 and PE6450 is lousy at best.  Be very careful when removing or replacing the Memory Riser Card.