Re-booting my iMac did nothing, so I tried v1.73, but with similar results. Other forums mentioned v1.70 as a good stable option, but again this made no difference to the problem. So this morning after much head scratching I thought I'd give v1.74 one last chance, and for some unknown reason it all works now!
Again, not sure what I did (haven't installed or updated any software), but now it is working again. Might be worth trying the above sequence as a work around (unless it was something to do with the full moon last night
