[slimonline]

Thanks for your quick answer...

Here are some more detailed information:

.) users got different internet providers
.) users got completely different hardware
.) no changes made in the last years from our site
.) already tried: re-installation + down- and upgrade of vpn software
.) already tried: re-starting the radius servers
.) already tried: disabeling the client firewall
.) already tried: talking to internet provider = no changes made by them

Thanks again, Florian