Naomi,

although I have solved my 'problem'. To answer your question: I had a field orignally formatted to '999,999.99 +' which was ok since it was at that time always an abs(value) and for clearity in the whole report a '+' was added to the figure to show it was positive. It worked like a charm.
Now things had changed and there could arise a situation where the figure would not be positive so adjustement was needed. So I needed an iif in my format. On second thoughts the other solutions is much better and easier for future maintenance. Thanks for your responses and enjoy the rest of your weekend.

Regards,
Koen