This is the problem: Enabling the network for Copperlan on my Mac Pro (Protools 10 HD)
has the effect that the ethernet connection between ProTools and the C24 controller get broken and the controller goes offline. This problem stays, even the C24 is direct connected by a crossover cable on the second network port and Copperlan is enabled for the first Port.
Btw: Audio-network applications like Vienna Ensemble Pro and MuseResearch Uniwire can be used without any problems.
Thank you for the help.