Windows 2003+ADS+ISA: Downloaders problem

[t304pk]

I am on a network; my server has ISDN and is sharing internet connection through ISA.
Server is managing user though ADS.
Until 3 days back, my server got Windows 2k Professional and my machine had windows server 2003 enterprise.
Everything went fine.
2 days back they upgraded to Windows Server 2003 Enterprise, too.
Now, everything else runs fine but only my machine can't operate any download accelerators.
I've tried FlashGet, MassDownloader.
It just says file not found.
While when I download from browser, it is fine.
If I configure my download accelerator to use proxy, it stuck at "Proxy connected. waiting for file...".
Got any idea?
Looking forward to your response.