CASE WHEN ({amount}-nvl({taxtotal},0)-nvl({shippingamount},0)) >3000 THEN 'Something' ELSE 'somethingelse' END

Formula(text) works when ungrouped, but I get the following error when trying to group

The result field Formula (Text) cannot be grouped. Please edit the search and omit this field or use a different summary function.

Any ideas?