Trying to vMotion a VM and it failed with the following error:

A general system error occurred: PBM error occurred during PreMigrateCheckCallback: No connection could be made because the target machine actively refused it.

Easy fix – ensure the Profile Driven Storage service is running on the vCenter server – in my case I had disabled it in an attempt to save resources on the vCenter server and I did not think I was using Profile Driven Storage functionality – so I thought!