Hi Henry,
This does seem to ba a MAC setup issue regarding permissions / administator rights etc or something on your network is blocking communication with your MC200.
You don't mention here what switches and routers you are using in your network, but there are some known issues with a couple of popular routers (BT HomeHub and some Tiscali units) which cause a plethora of strange occurences when used with MACs - Should you be the proud owner of such (or others to be on the safe side) I would check whether there are any firewalls / permissions etc blocking your MC200's path.
Good luck, and enjoy your Sooloos!
Sam