Error Copying large file on remote win 2003 DC via VPN

When trying to access large Excel file on a remote win 2003 DC via VPN, it
errors out. "Error copying file to folder - cannot copy file_name: The
specified network name is not longer avaiable".

I found this article on the net with a fix, but it only applies to windows
2000
http://www.linnetsol.co.uk/winxp.asp, see " Network File Errors After You
Install Windows XP SP1"

I am using Netscreen/Juniper VPN devices between site, the connection is
fine. I can copy and open the same file using FTP, no problem. I can also
attach the same file into Outlook/Exchange, it opens fine as an attachment.
If I put the file onto a Win NT4 server or a non DC win 2003 server, then I
have no problems accessing it. It only seems to be a problems when the file
is on win 2003 DC.
--
Andrew