TidFTP: "PUT"ting file sporadically hangs

I have an application that, among other things, frequently tries to PUT
a small (between 1KB and 21KB) file to an FTP server through a VPN. In
no appreciable pattern, the PUT often hangs.  Through logging, I can
tell that it "Connects", then changes directory, and then doesn't return
from the PUT.  I have a timer that waits 5 minutes and if the PUT hasn't
returned then it calls the abort method. When it does succeed, it takes
maybe a second.  When it fails, I have it retry a few minutes later.
This process has sometimes taken overnight, trying 50-100 times and then
it finally suceeds.

The problem occurs on all different size files, but I seem to see it
most frequently on files that are 3KB in size.

I have tried changing mode: "Passive" and "Normal". I have tried
changing Transfer type: "Binary" and "ASCII".

The problem occurs on an NT4 box.  I have tested it on Win98 & Win2K
with no problems.

Our network guy has seen "RUNT" packets coming from this box.  We think
there is a NIC card problem but of course the software guy has to try
all possibilities before the Administrator will do something like, oh..
putting in a new NIC card.

Using D6 Enterprise and the INDY components that came with them.
Upgrading to INDY 9 is not yet an option.

Any suggestions on fixing or troubleshooting this problem would be
greatly appreciated.

Thanks in advance,