For what it's worth and mainly, in case anyone should encounter the same problem, despite
being on the phone for hours to both Apple and Sound Tech, I have actually managed to
solve the problem myself!!!! Apparently error 748 means that the CPU can't cope with the
workload ... seems this was actually a red herring ... Logic (and Garage Band for that
matter) were freezing/crashing with this message on or soon after start up.
Turned out that a program called AudioXplorer ... downloaded from the Apple website was
causing HUGE conflicts! ... deleted all traces of this by doing a search for all the
far-flung bits and trashing them et voila ... happy Logic Pro 7.0.1!!!!
Probably need my rear end kicked for downloading the prog but it seemed a legitimate and
useful analyser ... learnt the hard way and have wasted four days or more of valuable work
time ... and that's with an otherwise Logic only machine i.e. no other programs ... just
goes to show!
Hope this may be of use for someone in the future.