if statement in access 2007 report

I have a report in access. in this report two columns for 'Wochenstunden' and 'Überstunden'. and their values 'Stunden' and 'Überstunden', which worked normally. then I changed both values as following:

=Wenn([Stunden]=0;'-';[Stunden])

=Wenn([Überstunden]=0;'-';[Überstunden])

(Wenn is the if statement in German form)

In the first one, it works perfectly and shows - when value is 0, but in the second one I get error(in report shows #Fehler instead of all values). Both columns are from same table and have similar values. what can the problem be?