I just downloaded the latest version of free Kontakt player 5.5.2, but it's giving me problems in Platinum (latest version).  It seems that I can only load one instantiation of Kontakt.  If I try to load a second instantiation, it crashes the project.  I'm trying to use Session Horns, and I would like to use 4 separate tracks if possible.  I've googled this and searched the Sonar site and have seen several others with problems but no solutions.  Am I missing something?  If I should have to uninstall and reinstall how do I clear the registry?  etc.  Thanks for your time.

Have you tried loading just one Kontakt player and loading more than one instrument in it? The full version can load multiple instruments. Also you should be able to output to multiple audio tracks. 

Hi John, yes I can load several instruments in one instance of Kontakt, but my performance bars start spiking and I get dropouts even at 1025 samples of latency.  I seem to have trouble with Kontakt loaded with any instrument.

Something is wrong with your setup. You have good system specs. You should not have any trouble. 
 
You may want to look at system latency to see if that is a problem. Be sure that nothing is loaded in the background that might interfere with Sonar.  

As for clearing the registry you can do a windows system restore to a date generally of your choosing. Before you loaded Kontakt.
 
Pay close attention when doing this, you sure don't want to do a factory restore or anything like that.