No idea why DSS is not working for you Raymo, but if you want to try other free stacking programs. There is available
Autostackert
http://www.astrokraai.nl/software/latest.php
and Iris
http://www.astrosurf.com/buil/iris-software.html
I've never used them, so I can't tell you if they are any good.
Cheers
Bill