Simple Currency Related Formula Not Working

Simple Currency Related Formula Not Working

I seem to be missing something with currency related formulas - I'm trying to do the following:

"input.Assessed_Land + input.Assessed_Structure"

Both fields are currency - it gives me the following error:

" com.adventnet.ds.query.QueryConstructionException: Datatype [CHAR] of the column [t_693811000000018081.Formula_693811000000025013] can  "

The error is cut off in the window - I cannot see the rest.

What am I missing?

Thx