When trying to join a vcenter to domain I was given the following error in the GUI

“The format of the specified computer name is invalid”

Turns out you can join the computer using a CLI , 

Putty into the VCenter and run

shell.set --enabled true

go to 

/opt/likewise/bin/domainjoin-cli join domain.com Domain_Administrator Password

I was then showed this : 

the hostname may not be ‘linux’ or ‘localhost’

Turn out the Vcenter DNS had been set to localhost.localdom ( due to it being added using an IP ) which it didn’t like. Changing the host name to the correct one fixed this