Thanks to BagginsBill and Gimp!

Yes, pressing the Spacebar does solve it!  (I'd be interestedto know why - it's just SO illogical!)

BTW, having done a reinstallation and then pressed the spacebar to get P8 working properly, in the process of establishing my preferred settings I kept getting a Poser program shutdown for no apparent reason.  This appears to be happening with increasing frequency and when it occurs the shutdown screen appears for between two and four times until the program eventually does shutdown.  I expect M'Soft are getting quite p....d off with Poser users reporting this so often!

Although I like P8 (and have got used to it's quirks like the one above) I can't help feeling that there is still something seriously wrong with it's programming for incidents like this to occur all the time