Wow that was stupid. Somehow I didn't notice that you could only move DINT with MVMT. Seems ... limiting. How can I move a REAL conditionally with fbd?
Also, regardless of that, the error message i am getting has nothing to do with that strangely enough, it could just be poor error checking, but it literally says that
Language element can not refer to a variable array index.
which, again, seems very strange to me.