So I can't quite figure out where in the get info panel it will tell me what the bit rate or sample depth of the video files is, but I've switched Sonar itself to several different bit rates and sample depths and changing them has no impact on the ability of Sonar to import video files.

nctowns
Well, I don't have windows media player—it apparently doesn't come native on the version of Windows 10 I have (Windows 10 N), ....
 It does seem that it's something in Sonar that is preventing it from working.

I have W10 Home on my laptop, and W10 Pro on my DAW and both have Windows Media Player installed. Shows up as Windows Media Player (under W) in the All Programs list. 
Anyway I agree it sounds like it is not likely a general Windows issue if you can play it in VLC.

Thanks for the response. Apparently the version of Windows 10 I have (Windows 10 N) doesn't come with it, though other version of Windows 10 *do* come with WMP

Try this: https://www.cakewalk.com/Support/Knowledge-Base/2007013354/SONAR-X3d-Switching-between-Media-Foundation-and-DirectShow-Video-Engines
 

may be related to this http://www.cakewalk.com/Support/Knowledge-Base/2007013353/SONAR-Launch-Error-for-Missing-MF-dll
 

Sounds like it Scook. To the OP - this suggests either switching to the directshow video engine, or installing the media foundation missing components should fix your problem.
Honestly never heard of Windows N before. Live and learn.

Well, it's just a version of Windows 10. I don't really understand the difference between Windows 10 N or Windows 10 K or Windows 10 KB. 

And I did switch it to the new video engine and it appears to work. I am able to import some video files. Still not all the video files I was able to on the old one, but some of them import and the ones I import into can import multiple video files without any errors and I can save and re-open them.

So I think I had multiple issues, but I think the most egregious one was the one fixed by your recommendation.

So THANK YOU! Thank you so much Brando and SKOOK. You guys rock.