Hi Marco,
well, I've got sometimes problems with DLookup, if it the search-string isn't found and so DLookup returns "NULL". So I use
myString = Nz(DLookup("FieldName","Tablename","Field2='" & var & "'"),"empty")
So myString = "empty", if DLookup is Null.
Maybe that helps.
Regards,
Mary H.