Thank you, choronr and Oshyan for your responses. I paused the render preview, an now I'm good to go.
It didn't happen unless I generated a terrain before adding a Power Fractal. Then, each time I tried to add the clip file, the heightfield would generate and it would put the clip file in the node area, then crash. Anyway, it works now. Thanks again, Bob..and Oshyan.
Linda