vCenter Error registering vmx

I was trying to bring an ESX host to maintenance mode, but it keep failing to migrate a box using vMotion. Being that VM the only one left, I suspended it and migrated it manually. Everything worked ok.

When I came back to that box to power it on again, this error showed up:

This virtual machine cannot be powered on because its working directory is not valid. Use the configuration editor to set a valid working directory, and then try again.