Hi Scott,
Why are you still running v15.7.6508 on the primary server? Upgrade them all to v15.7.6607 or (6600), as you are 4 versions behind. I always recommend using the latest build, seems to work most of the time in my case.
If you are running the built in clamav you need to upgrade to v15.7.6607 for security reasons anyways.
-dave