ok have some news in this topic, its really strange -.-
this doesn't depend on the multiserver, but on the channels that i'm joined, if i join more about 30 channels the dx-diag-test d3d fails
also clipboard and e.g. paint doesnt work anymore if i have many channels opened
if mirc is closed, all things are working without problems
so there seems to be a problem with the graphic driver and mirc, can anyone help me?