Really quick post
I was applying a Host Profile to an ESXi 5.5 host and it failed to add to the Distributed Switch.
The error was vim.fault.ResourceInUse.
The only link that I could find was one entry in the forums
The host was already in maintenance mode (per recommendation of the forum) but the profile (adding to VDS) failed.
What I started to think about was what is assumed when a host in maintenance mode? That there are no VMs on the host. Of course there were no running VMs since the host was in maintenance mode, but I clicked on the ‘Virtual Machines’ tab and saw four orphaned vms from some previous testing.
I removed the VMs from inventory, applied the Host Profile, and easy-peasy it added the VDS and everything completed just fine.