Proxy auth problem!

[jaqu]

Hi guys,
I have tried everything I know (including google), to fix this problem, and am not ashamed to admit that I dont know how to fix this.

Every 5-10 minutes or so, windows (or rather IE) gives a popup saying :
"Connect to proxy.proxy.co.za" with a correctly filled in username and password box. When I click cancel, it comes up again immediately . When I click ok, it goes away, and returns after 5 or so minutes.

PC's on the network needs proxy authentication to connect to the Internet. This pc authorizes just fine with the same username and password that is already filled in in the popup box, when opening IE and going on the internet.

This even happens if IE is not running. In fact, it happens if you dont run ANY apps.

So originally I thought that some process is running, and it needs to go on the net. But this has not helped me.

I dont know all the specs because its not my pc. But it is Win XP pro SP2.

What I have done sofar:
- Disabled Windows Auto Updates
- Upgraded form IE6 to IE7
- Set IE security lower and higher
- Changed setting in IE to "Automatically log on with saved username and password."
- Did registry fix
- Tried Hijack this
- Installed Spybot SD 1.52 and scanned
- Anti Virus (McAfee) is up to date
- Tried with windows firewall off and on
- Tried to see if any "funny" process are running in taskmanager, but didnt see any (although I guess I wouldnt know a good process from a bad one)
- Did a couple or registry changes I found on forums.

So from the list you can see that I dont know what is causing this.

Any ideas please I give up.