Exchange DAG Backup Fails with "Failed to Launch Proxy Master" Errors
In this case, the Windows Firewalls were on and there had been no rules created for the NetVault processes.
Workaround:
Add the following Windows Firewall rule to all of the DAG nodes (updating file path as needed):
netsh advfirewall firewall add rule name="NetVault MS Exchange Plugin" dir=in action=allow program="C:\Program Files (x86)\Quest Software\NetVault Backup\bin\nvexchangeserver.exe" enable=yes
