exchange replica vss writer failed

I have a 3 member DAG, two of the members are each backed up by a separate DPM server (one full backup, one copy backup).  Recently the copy backup server started having VSS issues.  The DPM server reports:

DPM encountered a retryable VSS error (ID 30112 Details: VssError: The writer experienced a transient error.  If the backup process is retried, the error may not reoccur (0x800423f3))

It keeps happening, even after I reboot both dpm and exchange server.

In the exchange server event log i get errors 2021 and 2112 for MSExchangeRepl saying the VSS writer failed with error code 80070015 when preparing for a backup.  I also get warning 8229 "A VSS writer has rejected an event with error 0x800423f3"

Any ideas?  The servers are all ex 2010 sp1.