Hi Marco,
Probably not a lot of use to you, but I have had quite a few issues with cards that were all supposedly compatiable based on the RTL8139 (?) chipset-most worked fine but a couple simply would not.
It may pay to try a few different cards-apparently Kingston cards are great. Mind you, the RTL ones I have been using from Trendnet are cheap enough to have a few lying around that I can swap in and out of boxes until I find one that works.