Visual Studio Express 2013 behind proxy

Hi,

I have downloaded and installed visual studio express 2013 for windows desktop (Version 12.0.21005.1 REL).

I'm working with windows 7 professional.

I'm also working behind a proxy with credentials.  Internet explorer is well configured with that proxy.

In visual studio, when I want to register or sign in, it tells me "Proxy Authentication Required".

Using wireshark, I see that the proxy server is well contacted but the credentials aren't send.

I also tried lot of configuration in the WDExpress.exe.config in the <system.net> and <defaultProxy>, but impossible to have something working.

It seems there is no off line registration, so what can I do ?

Thanks.