Erroneous error aggrigating different data types

Im getting an error message stating that I'm trying to aggrigate values of different data types, but I don't believe I am. In a table footer, I have a sum(fields!revenue). When I preview the report, the field says Errror, and the output window has a message that the field formula is trying to aggrigate different data types. The query column is a money type. The Report Service is interpreting zero value rows as integers and other rows as money or maybe decimal. If there are no zero value rows, the formula works. I've tried all kinds of conversion gimmicks to make the Report Service see the items as money, without any luck.

Does anyone know what I'm doing wrong, or know a work around?

Thank you,
Charles

The original description is wrong. The error occurs without zero values, too, unless all values are zero. The expression works in cells along the same footer row for integers and works on none of the currency columns. This is the expression: =sum( iif( Fields!Type.Value = "MyType", Fields!MyColumn.Value, 0 ))

It works fine for fields not of money type.