Actually. I'm not even sure that it's possible to use a calculation as a filter on a relationship that will return multiple results. All the examples that I look at seem to be returning single values
OK. Tried something else now....
Used the Filter Selector and added a Filter for the User relationship object drop down by clicking New in the Filter rules. I added the User Title field as a display and a criteria attribute. I then used the Is Not Equal To "CreateUser/Title" value and this worked.