I deleted my render directories, and also directories of older versions of my project so make a lot of room of my hard drive. Now I see that the pictures in my project are flickering/blinking. Is there any relation to the deleting of the render directories? How can I stop the flickering?

When you say "flicker", what do you mean?  Wide-to-narrow?  Narrow-to-wide?   Does it only happen when effects (pan-n-zoom, transitions) are applied?

Curious:  Have you yet tried enabling background rendering (if it's disabled) and letting everything background-render?  If so, does it then "flicker"?

BittMann

Is background render turned on or off?

If it's off, turn it on and watch the green bars.

If it's on, is the location for Aux files valid?

When I say flicker, i mean its like looking at a strobe light or a 70's disco ball.  I hope that helps.    I will check the background rendering and get back to you.  Thanks for your help.

Ok, I am happy to say that the blinking/ flickering has gone away.  I wish I could report why, but it just stopped.  

 Thanks to all who commented.

Thanks for the update.