The first things you should try are clearing your browser cache and using another browser. 

If you are inside Canvas and receive an "Application Error" message when you click on the Kaltura button in the rich text editor or try to add Kaltura media as an External tool, you may need to autorize a new token.  This sounds complicated, but it's simple to try. 

In the blue left-hand navigation in Canvas, click on the link to "My Media - Kaltura at Illinois" in the lower left.  

If working correctly, this would take you to My Media.   

If this is what's broken, you will be presented with a prompt to Authorize a new Kaltura token. 

Click Authorize.

After authorizing, you should now be able to embed Kaltura media in Canvas.