I've just gone through the whole thread again to remind myself. It looks extremely likely there is or was a hard disk error, and/or major corruption of the file system on your hard drive. An accident waiting to happen... Its very possible the two versions of windows interfered with each other.... ie windows 8.1 interfered with the BCD configuration or something.... Could have been the drive itself but more likely software... All just speculation but what was happening does really speak for itself.

Either way I can't see Sonar being responsible here myself...

The thing that really struck me were instructions I ran across for running sfc under Win 8.1 on WindowsEight forums, there were steps detailed for determining the boot drive and Win 8 drive in multi-boot systems and then formatting the command as this:  sfc /scannow /offbootdir=C:\ /offwindir=D:\windows
I understand the inoccuous nature of the command, it may also be the case that it could have been repaired. But my install disk didn't do it and I was in a hurry so I began reinstalling. I chalk most of this up to my lack of time to do it right, but I probably should have waited for CW's answer after X3 wouldn't start the last time. I hope you don't think I'm trying to blame it all on the sfc suggestion, not at all. It was eihter my lack of proper use, for not looking the proper use up, or somethng wrong that showed no symptoms at all beforehand as you suggest.

SFC /scannow will scan the windows you are currently booted into. It knows where everthing is once it has booted. Or if it doesnt it will stop. The other flags are when you want to scan operating systems that you are not booted in. eg if you wanted to scan a windows partition you have not booted up into..... which is offline.

I don'tthink Sonar had anything to do with the sys problem, you know you can't say for sure, the only issue I think for Sonar is why the PC add-ons stopped X3 from launching. That whole process: install PCs, launch fail - - uninstall PCs, launch - - install by each, launch until LA2A then fail - - uninstall, still no launch. It's unusual and I have no response from CW right now, not even a "it must be you", so until I do I'm on hold. I'm don't think your speculation is out of bounds either, but it does appear to me that win 8 was built to coexist with 7 since the MS site has plenty of info on dual booting them, it was automatic, and worked well. It would make sense in helping to convince people to adopt, as many are reluctant to leave the familiar. Can't rule out disc error either, and that may be most likely for the sfc error, but talk abut bad timing.

I just saw a couple threads with people having problems with 8.1, one of them had a problem with sfc being corrupt and it was suggested he check the hash on his download. I downloaded from MS but maybe I should check as well.

If you downloaded from MS store and installation completed successfully then you are fine...

I heard from CW support yesyerday and they tested the PC add-ons in X3 under Win 8.1 successfully. Also, the links to the updated PC add-on versions are now active on my download page. They download directly from the page listing my registered products instead of linking to a download page for the item, as the other links on the list do, so I'm assuming they fixed it this way.
 
Since they tested successfully, that makes the disk error / corrupted file problems the best canfifates for cause here. As Alex pointed out, this was already most likely, but I feel better with confirmation from CW of the testing in this environment.
 
I will be reinstaling Win 8.1 and X3, plus the add-ons, on a different HDD on Friday. I have fresh downloads of the add-ons on a new drive as well, so hopefully I will have better results.
I'll post the outcome after finishing and look forward to wrapping this up.

BTW sfc /scannow is just a way to see if Microsoft Window files are corrupted, not to be muddled with crc.
This and chkdsk are great ways to make sure you disk integrity and windows files are in tip top shape.
 
Always back up.
 
Cheers...

All of my files are on a sepearate drive, so I never lose thoe.
 
Looking back, I could have restored the Win 7 installation instead of reinstalling, I only lost that due to Win 8 boot mgr being gone but I didn't think. Apparently sfc was introduced with Win 98, but I never herd of it back in the day, a useful tool to keep in mind. I appreciate your help with this Alex, I've very lucky with hard drives through the years, save for a Toshiba laptop a girlfreind had that lost 2 in a row, so I guess I was due.

Reinstalled and everything is running fine this time. I haven't installed my 3rd party plugs yet, but they were already in before I tried to install the PC add-ons last time. I'll never know why X3 relaunched after the add-ons were uninstalled after the first attempt at installing them knocked it out, and the second time it didn't come back. I will point out also that although I installed 8.1 and X3 on a different drive this time, the drive they were on is now my Win 7 drive and running with no issues. It looks like a freak disk error during install, or that drive has a problem that will return soon.
 
Just for clarity, I did confirm through this that the updated versions of all the Pro-channel add-ons are the correct versions to install in X3 under Win8.1, in case someone has a problem and finds this thread. Thanks to all who chimed in and CW support for testing the issue, and Alex for taking an interest and giving direction. It's good to be back!