Normally this is one of a few things:
1. You're using a 32 bit build of Blender
2. You have some unofficial build of Blender that we don't support
3. Strange hardware configuration.
Can you check those three things?
Thanks for the reply
I'm using a 64-bit version - but it's one of the daily builds of 2.79 - (the 2.8 branch) - so maybe that's it(?).
As far as a strange hardware configuration ... I don't think I do - I have two Nvidia cards installed - but I got a similar error when I only had one card installed.
I'm guessing it must be the "unsupported" version of Blender. Unfortunately, I've gotten to the point where I use some of the newer features, so, I guess I'll wait until 2.8 is officially supported.
Thanks again for the reply