Holger
It does seem that you've done everything correct...
I can only suggest that you try using a different artnet interface if Olli's observations are indeed correct. Ive never had a problem with artistic lisence kit - it sounds like it could be a Schnick Schnack Systems issue??
I use a Luminex DMX node 8 for all my DMX-atnet communication. The software allows for change to the DMX refresh rate. Chech out Page 18 on the manual. THis may be a solution - but I've never tried it!
http://www.luminex.be/products/01000...r_guide_v3.pdf
Simon