But, until the member records of that group are rendered for the report, the sum in the header will be 0 (or at best the first record). That's one of the problems I have with crystal, it tries to do everything in a top-down, one pass method. It takes some creativity to get things to show up out of order.
Crystal passess through the data multiple times. Summary operations will print correctly in the Group Header. I do it all the time...