Mmmmhhhh... I see the various answers above and I realize that I still can't tell if you really tried to copy with a 64-bit copy program. (xcopy, robocopy and most FTP clients are 32 bit, even on a 64 bit Windows.)
Can you give it a try with the 64-bit version of TotalCommander V8.0 ? (It is still a Release Candidate, but very stable.) That is truly 64-bit only.
Another thing to try if the server has IPV6 enabled (usually does on W2K8): Disable IPV4 completely on the workstation so the copy will have to use IPV6. Will be interesting to see if that makes a difference.
If neither of the above brings relieve.... You can allways use HJSplit (or the split function of TotalCommander) to split the file in 1GB chunks, but of course you must have a means of re-joining them on the server. That will depend on if you have access to run a program on the server itself. (Just "copy /b chunk1+chunk2+chunk3 total.vhd" will do if you are not allowed to install additional software server-side.)