DPM failed to communicate with the protection agent on yourservername because access is denied. (ID 42 Details: Access is denied (0x80070005))Situation:
DPM Servers configured to protect each other, start denying access and refusing to connect. Servers are in the correct local groups (DPMDRTrustedMachines, DPMRADmTrustedMachines, DPMRADCOMTrustedMachines) on both the primary DPM server and the DR DPM server.
I don't have root cause on this yet, but not getting a good backup of your DPM Database is such a showstopper that I'm posting a cheesy work around.
To get back up and running, add the machine account of the DR DPM server to the local administrators group of the primary DPM server. This is obviously not a good long-term solution, but in my situation it's less dangerous than running with the DPM databases unprotected (your mileage may vary). When I've tracked down the permanent solution, I'll post it.