Problem solved, thanks teejay,
I moved the workstation to a different part of the network, from a different switch and Flash10 installed straight away, just as it should. After a bit of investigation it seems the port on the original switch is faulty, although I don't understand why it appeares to allow some communications/protocols but not others. It's not a managed swirch, just a common or garden Netgear job. Anyway all's well, so thanks for the idea of checking the logs on the client, that's where the clues were.
Steve.