Please, excuse the long Duration for the reply, but i have tested several Internet Explorer Versions and Locations.
The conclusion of my tests is that i can nearly use every IE Version and all of them do not work. Furthermore i have another interesting Information.
The Web Client is using an SSL certificate from the a programdata subdirectory which seems to be broken, because i can not open the rui.crt file anymore.
In the Program Files subdirectory there is another SSL certificate which seems to work allright, but the web Client isn´t using this certificate.
Firefox and Chrome are using the same broken SSL certificate, but do not bother about it.