Hmm...In this case I would start troubleshooting this issue from looking closer into VSS writers themselves. Windows Events Log should have more info in this:
singy2002 wrote:Within the guest OS on both servers when trying to query the VSS writers there is no output. (vssadmin list writers) the command just hangs.
Also if you could involve Microsoft support team into this that would help a lot.
BTW - can you please check VSS writers on one of the available successful restore points? Do you have the same behavior?
P.S. You can use On-Demand sandbox to isolate your Exchange Server from production network for these tests.