Are you using RunningTotal field or have you done yourself those formulas?

If you are using RunningTotal field, you cannot print it on Group Header. Running total calculates values you have printed so far.

Could you use some kind of formula or summary instead?

As EscApe said, you can't pass a running total to the group header area. The running total gets calculated as the detail section is being printed. Thus, the group header has already been printed prior to the running total even being calculated. So if you put it in the group header then it will always be zero.