Right-click context menu delay

When right-clicking a file on a previously mapped
network drive (i.e. - shows under My Network Places
NOT via Microsoft Windows Network tree)
to select Copy or something, I have about a 20 sec.
delay before the context menu appears.

If I browse to the same item via Microsoft Windows
Network, etc, etc, - no delay.

What's going on during the 20 sec. and what can I
do to kill it?