The Problem was the MCAfee Virus Scanner. McAfee told us to unregister a dll of the Virus scanner (SCRIPTSN.dll). And now it works.
Note: SCRIPTSN.dll is a Browser Helper Object (BHO) that runs automatically every time you start your Internet browser. On older Windows systems like XP it was possible for malware to pretend that it was SCRIPTSN.dll. On startup ACE 3000 will attempt to access our web server to detect if there are any new updates, news, tutorials, or other helpful information.