Edit Patch Window Won't Launch

Hi,
I'm new to M4L but have been using both MaxMSP and Live for several years.
I have just bought M4L and and having no luck whatsoever in launching the edit window from Live - The button turns green and flashes and the Live status bar indicates "Starting Max Editor". Max itself launches but no patch is loaded or windows appear.
I am sure it must be something simple bt have been trying for two days now to no avail.
Does anyone have any ideas at all?
I have Live 8.1.3, Max 5.1.4 on OS X 10.5.8
Cheers and thanks in advance, this looks like a great resource!