I seem to have come up with a solution – though the raid is still occasionally unstable (it removed itself again while rendering causing ‘a device removal’ warning, after I had come up with the solution described below).
I suspected that it hand something to do with a corrupt file in one of the scratch folders. By removing all of them FCP opened fine. I then reintroduced the originals one by one (restarting FCP each time to check). Seemingly it was the the render folders that contained the problem.
However I still think that there is a more general fault relating to the Media Raid. I’ll get in touch with the manufacturers as suggested.
Have you come across something like this before?
Thanks again,
Shane