Anderton
One question remains: If you keep loading instruments into Kontakt until you do run out of memory, does it generate the same error message? NI might find that information helpful. 

I successfully loaded multiple large instruments into a single instance of Kontakt in Sonar X3e by using the enter key instead of the mouse (see my previous post). I pushed Sonar's memory usage up to 3079 MB without any problems. At that point I was at only 73% memory usage in Windows but I gave up because it seemed stable enough.

robert_e_bone
Please list your computer specs - CPU type, memory, etc - you can look at my signature at the bottom of this post for an idea - ideally you will want to add your specs to your forum signature, so that folks can get an idea of what you are running with when they are trying to help you debug some weirdness.  :)
 

I just added them to my profile. Hopefully they will show up on this message.

Thanks again for the help everyone. I don't know whether the problem is Sonar or Kontakt. I'll make sure both tech support teams get this info.

It sounds to me that you have identified the problem. I would add that you may wish to put your mouse on a USB 2 port if you have one.  

John
It sounds to me that you have identified the problem. I would add that you may wish to put your mouse on a USB 2 port if you have one.  

Unfortunately it's not really a good option for me. My laptop has one 2.0 port and two 3.0 ports. My audio interface is going into the 2.0 port and my external hard drive (for samples and audio) is going into one of the 3.0 ports. I prefer to have each of these on a dedicated port. My keyboard, mouse, MIDI controller, and other peripherals are sharing the second 3.0 port via a powered, 7-port, 3.0 hub.

Silhan

John
It sounds to me that you have identified the problem. I would add that you may wish to put your mouse on a USB 2 port if you have one.  

Unfortunately it's not really an option. My laptop has one 2.0 port and two 3.0 ports. My audio interface is going into the 2.0 port and my external hard drive (for samples and audio) is going into one of the 3.0 ports. My keyboard, mouse, MIDI controller, and other peripherals are sharing the second 3.0 port via a powered, 7-port, 3.0 hub.

Try to reinstall that hub. That means uninstalling it and reinstalling it. The audio interface wont work in the USB 3 port? If it will why not move it there and move the hub to the USB 2 port?
 
You have been very cogent in your responses.
 
At any rate I wish you luck!

John
Try to reinstall that hub. That means uninstalling it and reinstalling it. The audio interface wont work in the USB 3 port? If it will why not move it there and move the hub to the USB 2 port?

I'll try switching them to see if it has any effect. My reasoning was that the 3.0 port would give me a higher bandwidth so that all of my 2.0 devices could run at full speed. The audio interface is only 2.0, so I don't expect it to benefit much from the 3.0 port. I suppose my keyboard, mouse, and MIDI controller could share the 2.0 port since I generally don't use them all at the same time. One thing I didn't mention before is that I have an external Wi-Fi adapter connected to the hub as well because my internal Wi-Fi adapter is flaky. But then again, I don't expect to use Wi-Fi at the same time that I'm using the MIDI controller so it may not be a problem.
 

Let us know how it goes. 

John
Let us know how it goes. 

I tried it but unfortunately it didn't make any difference.

Make sure you disable the external WiFi adapter in windows (right click it) when you are not using it or unplug it. I assume you have permanently disabled the internal WiFi (ideally in BIOS if there is such a setting otherwise disable the adapter in windows).
I guess you could try to work this out via a process of elimination by disconnecting devices one by one.
Couple of questions. Are you using any special mouse drivers or software you installed for it? And what antivirus are you using?
 
Cheers..