Insufficient resources to satisfy configured failover level for vSphere HA.

I encountered the following error message while attempting to turn on a FT VM in my lab environment:

Insufficient resources to satisfy configured failover level for vSphere HA.

While in a production environment you should obviously remidiate this as soon as possibe, although as a temporary workaround you can disable the Admission Control by going to:

Inventory >> Hosts and Clusters >> Right-hand click the Cluster >> Edit Settings... >> vSphere HA >> Admission Control >> Disable.