How to fix scale Key-framing issue
It looks like you machine might just be too slow to live render the effects. The red bar on your timeline is an indicator of that. Try selecting the clip in the timeline after you add the scale keys, then from the menu bar choose Sequence &gt; Render Selection. After that renders out, the red bar in the timeline should change to green, and you should be able to play the preview video.

If rendering each effect before preview isn't an option, or is just too slow for you, you could also try changing the playback resolution in the Program monitor. That's the small fly-out menu under the main preview area that currently says Full. You can change that to 1/2 or 1/4 and it can significantly improve the live render capability of your machine. Everything will look more pixelated during preview playback, but it won't affect the final exports.