More Grouping Questions - Sum Of Maximum

I have a table with two groups, unit and domicile. Structure appears as follows:



GH1 - Domicile Group: Bentwood
GH2- Unit Group: 200
Detail: LegID Unit ID Miles TripMiles
1 200 25 150
2 200 75 150
3 200 50 150

Subtotal for GH2 Count(Fields!legID.value) Sum(Fields!Miles.value) First(Fields!TripMiles.value)
3 150 150

This works, what breaks is the subtotal for GH1. on the TripMiles Field.
It doesnt like Sum(First(Fields!Tripmiles.value,"Unit_Group")), nor can I do Sum(ReportItems!Trip_group.value) I get the error that an aggregate cannot occur on a report item unless it is in the page header or footer.

Of course if I try Sum(Fields!TripMiles.value,"Domicile_Group") I get 450 which is incorrect.

I've tried making First(fields!tripmiles.value) a calculated field which I just then drop into the header of the Unit group<GH2>. This works perfectly until I then try to Sum that field in the Domicile group. I can create the expression but once I click ok, VS2005 reports that it must shut down and crashes to desktop, when I do a recovery all my changes are lost.



<by the way this crash always occurs when I create a calculated field that uses First/Max or Min, then try to use that field in another calculation. Fields based on IIF work without issue>


To clarify, I want to take the TripMiles Column and for The Unit group show the first value that occurs for that unit as the value.

In the Domicile Group, I want to sum all of those Unit Values.
if unit 200 had 3 occurances of 150, my Unit group would have a value of 150 <not 450>
if Unit 300 had 4 occurances of 100, my Unit group would have a value of 100 <not 400>
My total for the Domicile would be 250 <not 850>

Thank you for any assistance.