This one comes on foot of a thread on the Minasi forum related to how AV screwed up a VM on a Hyper-V host.
My recommendation is to not put antivirus on a Hyper-V host. Unfortunately there are times when the techies get overruled on that one. If you have to install AV on a Hyper-V host then you must read every word of this page. It deals with how to avoid the dreaded 0x800704C8, 0x80070037 or 0x800703E3 errors when you start up virtual machines. Do not skim over the page, do not make any assumptions about knowing where VM files are, do not undervalue the “shortcuts” you might see, and be aware the hidden folder that is referred to. Long-time readers might remember my first W2008 RC Hyper-V lab host and how a bunch of VM’s disappeared on me. This was caused by AV scanning the VM files (including those “shortcuts”) after a host reboot. The VM’s disappeared from the Hyper-V console, even though all the files were still there.
In a more general AV & Windows conversion, you should also pay attention to Microsoft’s doctrine on AV exclusions for enterprise deployments of Windows. A long time ago, I had a Sysvol issue on a few DC’s in branch offices. We ended up believing that our AV caused the issue. Check out that site when you are putting in AV or configuring scan exclusions.