There might be several reasons for this as we have seen in the past bug fixes.
Anyway it makes more sense to open your own thread instead of pulling one marked as answered and very aged (old Windows and old WHS!) up. Therefore I will split this thread.
Did you apply all available updates to WHS? Network card drivers are up to date? How is the machine in question collected - via WLAN or wired?
Could some antivirus suite installed on the client intercept?
Best greetings from Germany
Olaf