I had the same problem. I installed Kontakt 4 and it didn't show up when I was running Logic in 64 bit mode.
So, I started Logic in 32 bit and it was able to recognize Kontakt 4.
Then I started Logic in 64 and it too saw Kontakt 4. Must be it needed Logic 32 to see and connect to Kontakt 4. Since then all is working well.
Hope this helps.