I have an instance of Kontakt (5.8) that had been hosting three instruments. It had been working fine and I was about to freeze it when I noticed nothing was playing back on those tracks. I opened Kontakt to check it out, thinking I might have accidentally re-routed the MIDI or muted the instruments or something dumb like that.
 
To my surprise, what I saw was a blank UI that showed 0 bytes loaded and it was not responding to the onscreen keyboard.

If I load another instrument, it shows up but won't play. Nothing I load into this Kontakt instance (NI-registered or not) will make a sound. 
 
However, I can load Shimmer 'n Shake into a new Kontakt instance with no problems, so I know that particular library isn't broken. The project has 6 other Kontakt instruments and they have no issues. So I do have a workaround (delete and replace), but I'd sure like to know what happened because this was quite an annoying inconvenience - I'd spent a long time building those percussion sequences and tweaking instruments. 
 
Thinking maybe I'd run out of RAM, I froze the other virtual instruments and rebooted the computer. The problem persisted, so it's not a case of running out of resources.
 
 
Just in case this is a new Kontakt bug (or potentially even a Cakewalk bug), I'm going to start saving all my Kontakt instruments as snapshots until I figure out what happened. For the moment I'm shutting down for the night to sleep on it. Hopefully, one of my fellow longtime Kontakt users will greet me in the morning with some helpful insight...
 
 

Hi Dave,
 
Sorry to hear about that problem.  I've never seen it myself.  I'm on Linux at the moment so couldn't tell you what version I've got installed (On edit: 5.7.1).  Something that you're doing differently from my use is hosting multiple instruments under one instance. 
 
If you haven't already, you might want to fire up Process Explorer and follow what happens as you load your DAW, open the project, etc.  I've also attached debuggers to running processes (fire up DAW, attach to process, open project, etc.).  Even without source you can sometimes get hints as to what is going wrong through warnings and error messages.
 
It looks like the project file has gotten corrupted or something like that --- a corrupted link or filename, folder name inside the project file ???  This may show up in the debugger, or it may be possible to repair the project file, although in my own experience, the latter is close to impossible due to lack of documentation on project file formatting.  You may want to look for malformed strings in there, though.
 
Please do let us know what you find, if anything.  You've probably already done most or all of this, but I thought I should post anyway.
 
Best regards,
Dave Clark
 
On edit: I found the following when looking for "vst," "corrupt," and "chunk":
https://www.native-instruments.com/forum/threads/kontakt-5-unexpected-data-chunk-file-corrupt.218228/
The resolution to the OP's problem was that he had updated recently, resulting in conflicting dll's.  Removing one of them allowed loading of the correct one. Another user had a similar problem with a "corrupt chunk" type of message and conflicting dll's.

You do run into some interesting "opportunities to troubleshoot!"

I've not seen this directly, but my alter ego provides technical support for a library developer, and I have had two people report a problem that sound frighteningly similar to your description.

In both cases their library installation was corrupted. In the first case the  library had worked, and then stopped. The used tried several libraries and discovered that some worked reliably, some did not. As I had no better advice I suggested reinstalling, and that did the trick. No idea what happened, Kontakt does not (generally) write to those directories.

Second time around it was a new installation, and I jumped (successfully - go figure) to a conclusion that the installation was bad. It was.

I certainly would not put money on this based on two instances, but if you still have the installers it might be worth a try.

This just keeps getting weirder.
 
Today, I can't even load that particular library in a brand-new empty project.
 
However, I can load it into standalone Kontakt, and I can load it in Samplitude, so the library itself doesn't appear to be broken. 
To be certain, I completely re-downloaded and re-installed Shimmer Shake Strike, thinking that perhaps a resource file might be corrupted. That didn't change anything.
 
 
When loaded in Cakewalk or SONAR, the UI is empty as well as the Script Editor's GUI tab. The Mapping Editor and Wave Editor, however, show that samples are being loaded. Everything's there except the graphical elements. And nothing plays back.
 
Process Monitor yielded no clues. I had intended to capture success and failure snapshots for comparison, but since I can't load the library in Cakewalk anymore that isn't possible. All I could do was read through the the thousands of actions and look for failures. There were some registry keys that it tried to open but don't exist (e.g. HKLM\SOFTWARE\Native Instruments\Shimmer Shake Strike\serialNumber), but that's not unusual. If those keys were essential, it would have also prevented opening in standalone Kontakt. It had no problem opening license and resource files.
 
 
 
 

Dave is it possible that you upgraded anything in that NI instance. I had a vaguely similar issue with a wave plug-in in Presonus. Everything looked fine but was not working on one channel. I eventually deleted and added the same plug-in and it started working. I had updated the waves plugins a few days before I noticed the problem. Just a thought.   

Thanks for thinking about it. I have deleted the Kontakt instance and inserted a new one, but the problem persists. I have opened a fresh project but it still comes up blank.
 
I don't think the library is broken, as I can load it in standalone Kontakt and in Samplitude. The issue only shows up in SONAR and/or Cakewalk.
 
I did update Kontakt after realizing I was running version 5.7. But the problem showed in both 5.7 and 5.8.

Some plugins use the host to communicate on the network for authorizations, etc.  I have seen instances where if I blocked my DAW in my firewall, I could only authorize a plugin via their standalone app that was allowed net access.
 
Is Cakewalk/Sonar allowed outbound network access through your firewall?

At last, a clue, and an apparent resolution...
 
I found that it only failed in SPlat or Cakewalk if, when I insert Kontakt, I didn't tell it to create MIDI and audio tracks. If I let it create the tracks, the library loads. If I then route the original MIDI and audio tracks to the new Kontakt instance, the instrument plays.
 
However, as soon as I delete the now un-needed empty tracks that were created when I inserted Kontakt, the instrument goes silent. If, instead, I copy the MIDI data from the original track to the newly-created ones and delete the original tracks, then all's well.
 
Conclusion: there was something corrupt with the original MIDI tracks. Not the MIDI data itself, but something internal to the project file. Did not see that one coming.

abacab
Is Cakewalk/Sonar allowed outbound network access through your firewall?

Curious thing I noticed while running Process Monitor: Cakewalk is constantly talking over the network. So much so that I had to filter out TCP events to prevent them from filling up procmon's display. Another day, I'll have a peek and see what it's being so chatty about. I suspect it's the debugging features I enabled when I started participating in the beta program.

bitflipper

abacab
Is Cakewalk/Sonar allowed outbound network access through your firewall?

Curious thing I noticed while running Process Monitor: Cakewalk is constantly talking over the network. So much so that I had to filter out TCP events to prevent them from filling up procmon's display. Another day, I'll have a peek and see what it's being so chatty about. I suspect it's the debugging features I enabled when I started participating in the beta program.

I've been messing with the new GlassWire Firewall app, that is really just a front-end for the Windows Firewall.  But it has a handy "Click to block" and  "Click to allow" feature to control applications for outbound net access.
 
It also has a nice usage monitor so you can keep up with what connects where.  It is just amazing how chatty modern apps can be.  If I'm in any doubt, I just go down the list and "Click to block" them.  If they still function afterwards, I leave them that way...