I have two DPM 2007 servers, DPM1 and DPM2. DPM1 is onsite and protects my servers using disk-to-disk. DPM2 is offsite and provides secondary protection for DPM1 using disk-to-disk. Everytime DPM2 attempts a recovery point of DPM2, the job fails, "DPM failed to communicate with the protection agent on DPM1 because the agent is not responding. (ID 43 Details: Internal error code: 0x8099090E)". I googled the error and found that a hotfix is available, however, I'd already applied this hotfix to both servers. I found that after a few days of recovery points failing, if I run a consistency check, the consistency check will run fine without any problems (the replicas are also created without issue when new members are added to a new or existing protection group). Again, I searched the internet and found someone else who appears to be having the same problem, but I don't know how/if he resolved it.
On DPM1 random jobs will randomly fail, usually with the error: "DPM failed to communicate with the protection agent on DPM1 because the agent is not responding. (ID 43 Details: Internal error code: 0x8099090E)". Which strikes me as odd, but at least it seems like all of my woes are caused by one software component rather than dozens. I searched google for "DPM 2007 server agent unstable" and found an article where the author dives into a hotfix recently (at the time) released. This article describes a behavior where logging into a windows 2008 server running hyper-v for the first time after a reboot causes the system to hang at "welcome". DPM1 does this to me so I kept reading and saw that his problem was that DPM was causing VHDs to be mounted/dismounted frequently leaving orphaned registry nodes which increased the registry size which caused the system to hang at "welcome" for several minutes or hours. I read the KB article he linked and saw that this is easy to spot so I looked at my registry and found none of the thousands of orphaned entries indicated. I did check the file size of DPM1's system hive against that of DPM2's system hive; DPM1 is 120MB vs DPM2's 13MB. So I have found an issue to fix, but I'm not sure its related to the protection agent.
I continue to search the internet for a possible solution, but anyone else who seems to have the same problem seems to have abandonded their original forum posts.
Some environmental information:
Windows Server 2008 R2 Standard
DPM 2007 SP1 2.0.8868.0
This server is a Hyper-V VM
Windows Server 2008 SP2 Standard 32-bit
DPM 2007 SP1 2.0.8868.0
This server is a VMWare VM