Hyper-V VM won't back up without being in a saved state

I have over 50 VMs in a cluster, and they all back up just fine. But this new VM I just built gives me the error that it has to be put in a saved state to back up. This is not a server that I can have going into a saved state every night. What could possibly be causing this on just one VM? I've tried rebooting, moving to another cluster server, same issue. No vssadmin writer errors anywhere, I'm stumped.