VMware error: Could not fix soft vm/host affinity rule violation

The Cluster contains no hosts satisfying the soft VM/host affinity rules constraint for VM

I came across this error recently that baffled me for a few minutes. I've several DRS Rules which cover Stretched Cluster Datastore/Site Affinity to ensure Uniform configuration but also some Database specific ones to pin VMs that use Application level replication and don't need to move around as much. I had a few test VMs and two were affected:

I checked the Rules and everything seemed fine but then I remembered I had a problem with hung VMTool Upgrades and sure enough the two VMs had the issue. I manually ended the VMTools installation so it released the CDROM and ran the DRS job and both VMs migrated to where they should have been. As they were mounting Host specific ISOs they couldn't go anywhere until this was rectified.

Might help someone else out! I've since updated the VMTools in the Template where they came from the resolve once and for all!

Cheers
Michael.