To answer my own question, the problem is with M-Audio, not Logic Express. The latest M-Audio driver does not equip the Firewire 410 to deal with Mountain Lion. Strangely, one of the older ones seems to cope just fine. If anyone else has these problems try this driver, which is meant to be for Mac OS 10.6.8 64-Bit, Mac OS 10.6.8 32-Bit, Mac OS 10.7.4:
Fingers crossed that M-Audio will eventually get round to updating their drivers properly.