Windows 2008 Server - unable to copy files from server to another machine; reverse works fine

Hi!

My Windows 2008 Server started acting up on me all of a sudden.

Every time I try to copy a larger file from it to a network share on another
machine, it freezes, reporting that the local file I am trying to copy
cannot be found ("Item Not Found" error dialog", or that there is a network
error accessing the local (!)file. Sometimes the copy works a bit at the
beginning, then the speed crumbles to < 10KB/sec, and the errors pop up.
All machines are in a Windows 2003 AD, the 2008 box is a workstation, not a
dc server.

I managed to disable all advanced tcp features (RSS, Chimney offload,
receive windows tuning, congestion control), and now I can at least transfer
files to a Windows 2003 server (slow; 4MB/sec). Transfering to vista x64
(also with modified txp features) still doesn't work.

What's funny is that going in the oposite direction - putting the files onto
the windows 2008 server box - works without a hitch. From the Vista box it
goes with cca. 11 MB/sec.

Any hints on how to fix this? The 2008 Server is my primary development
workstation and this is a *major* pain.

Thanks & Best Regards,

Sigmund