[AccessD] Using Sum to add total without duplicates

Hey lIsters,
My first post with my new address and I think it's easy, I just have to
get up to speed.  I have a report that does a sum([ErrorAmount]) at the
footer.  ErrorAmount is in the detail line, however there are duplicates
which are incorrectly being added to the sum([ErrorAmount]).  Any
suggestions?

Thanks,
Randy.