You must have a gpu accelerated video card otherwise you would not be able to switch to MPE software only.
Which video card do you have installed and do you have the driver up to date?
•For Windows, do NOT rely on Windows Update to have current driver information
•-you need to go direct to the vendor web site and check updates for yourself
•ATI Driver Autodetect http://support.amd.com/en-us/download/auto-detect-tool
•nVidia Driver Downloads http://www.nvidia.com/Download/index.aspx?lang=en-us
Thanks, Ann. As I mentioned in my post, Tushar correctly pointed out that, without a GPU accelerated card (which I don't have - mine is a piece of junk which I will be replacing with a compatible one soon) you must use the software only settings. I had changed my project over to the 'software only' setting, and I still had the problem. The value Tushar added was the procedure for clearing the cache.
What I did originally was a newbie error, no argument. I posted it here for others who may fall in the same hole. Your reply confirms that, without a GPU accelerated card, use the software only settings (sounds so obvious, yet I missed it.....).
Thanks, John. Great point that the drivers are always an important area to check. In this case it was my ignoring the obvious in setting up the project, and thereby creating a downstream problem that required clearing the Adobe rendering cache. What you have said is a very sensible route that can only make things better.