[Owncloud] Proxy-firewall denies windows-client

[Michel Kunkler]

Hey!
I would like to setup the owncloud-windows-clients in a company. (The 
companies internet goes through a firewall)
I have a nginx webserver set up and I can connect to owncloud using the 
windows client from home.
However, when I connect from the company, the windows-client gets http 
error 403 (forbidden) responded.
Therefore I can still use the webclient in the company though. I made 
some screenshots of wireshark sniffs where you can see the difference, 
between the access:
https://www.dropbox.com/sh/4tu6ftcnhogfogi/YWvfL6vwIG
(I hope you excuse dropbox ;) )
Watching these files lets me assume, that the http user-agent might be 
responsible for this firewall behaviour.

Does anyone have further informations for this kind of problem?