Property Calculator: Error Case if two actors are the same

Good afternoon,

I think this is a fairly straight forward one but I haven't been successful to execute it, so far.

So in one of our Requests, a Requestor can specify the main "Traveler". They must also specify the "Line Manager" who will approve the Travel Request.

Both properties are based on the organizations employees.

I want to prevent that the Requestor is even able to create the Request IF the "Traveler" and the "Line Manager" are the same employee.

I guess I do this from the Property Calculator "Error Case".

Given this, I specified that a error is generated if "{Traveler} = {Line Manager}" (see screen capture).

However, the tests I am running are still allowing me to modify and save the document when "Traveler" and "Line Manager" are the same, so the error case is not working like I intended.

Can someone kindly point out the solution?

Many thanks!!

Patrick.