HttpResponse Redirect does not work with Internet Explorer behind proxy

[Ludwig Hinske]

Dear group,

I hope you can help me get an idea about where to search for a solution to my problem;
The application I developed displays a login-form on the start page. When the user successfully
logs in, the Django view returns a HttpResponseRedirect object to the members area view (views
protected by the @login_required decorator).

The webpage works well an all major browser (Firefox, Chrome, Safari, IE 8 - 11). However, if
the Internet Explorer is located on a client computer behind a proxy (or using an anonymous surfing
VPN tunnel),  a "Internet Explorer cannot display this webpage". Firefox, Chrome, and Safari are all
running fine behind the same proxy. Unfortunately, it is important that users can access the webpage
using IE behind a proxy.

Does anyone have an idea, what the problem could be or how to get rid of it? Since I have no clue,
where to start looking for a solution, I'll be posting "configuration on demand" :-)

Thanks a lot in advance to all of you,
  Ludwig