A question marks is normally the replace-character of qlikview if any value has no string-representation. Therefore you should get a visible output if you used functions like text(), num(), dual() and/or to check them functions like len() or ord(). But this is rather not a solution else a workaround respectively a way to find out what's going on.
I think you need to check again if really all settings to the char-set are the same. This also includes the various windows-settings, for example the region-settings then qlikview will use them. Here an example what is meant and what might be related to your case: Search - But what shall you find?
