Can't see your field names, but assuming you want to sum the distinct counts that you inserted at the group level, create a formula like this:
//{@dcnt} to be placed in the group header section and suppress the formula:
Whileprintingrecords;
Numbervar dcnt;
dcnt := dcnt + distinctcount({table.field},{table.groupfield});
In the report footer, add a formula like this to display the result:
//{@displdcnt}:
Whileprintingrecords;
Numbervar dcnt;
-LB