> Maybe a long shot, but check the firmware in the 2424M is up to date.
> There were some issues like this fixed in various HP firmware releases
> - the one I remember was related to their gigE module, but you never
> know.
>
> http://www.hp.com/rnd/software/switches.htm

Many thanks for the help - it turned out the software on the switch
was several years old.  I uploaded the latest version and the
connection worked immediately.  I'm now going back through the release
notes to find out what the problem was.

Thanks again :)

Tim