Your variable controlled unit is set on the rpc server. So the server is set. The client isnt set because the variable isnt replicated. Click on your controlled unit and set it to replicated in the properties. So your variable should now have two white icons in the event graph.
The reason it didnt work because it wasnt valid and you have no pins connected to not valid. A good thing I do whenever I cast to something or do an is valid I put a print string node on the server to say what failed if it does fail.