Thanks Don,
I tried installing the runtime separately, but the error showed up anyway. I will look into DebugDiag tomorrow.
The customer is trying to open a support case with MS for the issue as well.
I am not that familiar with App-V, the customer is the expert there. I have a test system set up and we did a session together to duplicate the issue.
The gut feeling I have is that it is the change from Q:\ in 4.5 to %AppData%\Reallylongguid\Anotherreallylongguid that is the root issue, but why the regular client works and the RDS one does not is beyond me.