FWIW, I had a similar problem some versions back with screensavers that use a
'Ripples' effect which my video or video driver didn't like. That problem
went away for me with Version 7.0.5.

If you are using the standard Knoppix screensaver, which rotates randomly
through many selections, you might want to selectively remove some of the
selections to see if you can localize your problem to just a few selections
as I was able to do.

Also don't forget to do a testcd on your LiveUSB if that's what you are using.