The GTX 970 does work. I have 2 of them. It's possible there's something in that scene it doesn't like. First try rendering one of the included scene. That will eliminate some kind of hardware issue.

If a simple scene renders but not the scene you're having problems with it could be there's a material setup in that scene that's making the GPU unhappy. If this is the case we'd like to get that scene in the support system so we can track down the exact issue.

If it's just the one scene, go to https://support.posersoftware.com/ and create a support ticket. Use Poser 13's scene export (File > Export > Save for sharing ... ) that will create a scene complete zip file that can be attached to the ticket. If it's too big to attach we can provide an upload link for your scene. We can use that ti try and isolate the problem.