Hi Kane,
It is important to understand that the error as shown (everything after "ShowDataList:") is the actual error coming from the database. Especially because this is an advanced query, the Platform version has nothing to do with it. Also, the error clearly shows what's wrong, you are trying to subtract two columns that aren't numeric, as others already have suggested.
That said, the query itself is also very fishy, since you are doing a full outer join of the two Entities, having them both in the FROM without any WHERE condition.