Region 1 DVD drive refuse to run right DVD

Hi,

I hope someone might have an answer to my problem:

moved to the US a couple of years ago, so I bought a used PC (cause of voltage difference) with a Pioneer DVD drive to play US (region 1) DVDs and included my former LG drive, to keep watching my old European (region 2) DVDs.

So far so good, this worked fine.

Now, I moved back to Europe, got a used PC here and included the Poineer to watch the US DVDs I got in between. Drive is recognized, is listed as Region 1 in preferences, but won't load content from US DVD!

More interestingly, I am able to play Region 2 DVDs. Is there anything else I habe to set up software (XP) or hardware wise?

Tried uninstall again, reboot, got detected correctly, reboot, no change (doesn't recognize reg1 movies)

Thanks for any hint,

Cheers, Christoph