Hi.  Firstly many thanks once again to those who have replied and all the useful advice you have given - it is very much appreciated.

It looks like a RAM upgrade is needed plus the modifications to the Poser programme that everyone has suggested.

For additional reference to all the problem has only ever occured when I have been working with one figure on the screen, never two (never tried to create a picture with more than one figure before) and the error message has appeared on the screen in most cases before I have even got to the rendering stage.