OK, so I found out about the death of SONAR about a month ago, but haven't had time to scope out either Samplitude Pro X or Studio One Pro cross-grades I bought. Reality bites, you can't buy time ...
 
Anyway, I just tried creating a new project to mix my last gig capture in SONAR.  I got the dreaded "disk may be full error" and another about a bad parameter; reboots don't help, making a new project doesn't help ...  The DAW PC has tons of disk space; it's fine. It'll open an play the old SONAR projects just fine. 
 
Anyway, SONAR is already having issues, I can open old projects and play them,  but cannot import WAV files into new projects - FRACK!  Time to scope out the cross-grades I bought, eh? I thought it might continue to work just a little bit longer. 
 

If it's not just your HD going bad, try the usual tests at:
 
https://www.cakewalk.com/Support/Knowledge-Base/2003187/Audio-Disk-full-unable-to-save-entire-recording
 
The reason I mention your disk is because it can read but is having problems writing, which can signal the beginning of failure.

I would guess that it's something system specific, over here I 've got Cakewalk Home Studio 2004, (released in late 2003), and Cakewalk Guitar Tracks Pro 3, (released in early 2004) both installed and running on windows 10 64 bit on both my desktop and my laptop, the old VST adaptor program doesn't work, but the core programs and the old basic Cakewalk DX plugins are working fine.

The plot thickens ... My legacy SONAR X3 is having the same issue as Platinum on the same DAW. It can't import the new WAV files either.  So, it may not be SONAR after all, perhaps Windows Update killed my DAW. The odd thing is that the new WAV files that refuse to import are recognized in Windows as valid and play when you double click on them.

Could the files be importing way to the right on the timeline? If so, they are broadcast wav files and SONAR is set to Always Import Broadcast Waves at Their Timestamp.

I think you are probably correct. I currently suspect that it might be a CODEC problem. It was recorded on my PA System's PC connected to my X32, and I'm trying to import it into my DAW in my studio.
 

If there's a serious issue with Sonar then we would have loads of people coming here with the same problem. Anyway hope you are backing up with something like Acronis True Image.

Thanks for the tip, I checked, and they are not Broadcast Wave format.
 
The frustrating part is that I'm just trying to do something I've done repeatedly for the past few years successfully. 
 
I suppose the fact that I left the PA System off of the internet for six months could be an issue, it didn't get any Windows Updates, I suppose that somehow my two PCs are out of sync in the codec department. 
 
 

All of my important PCs have battery backups and scheduled Acronis backups, although, this feels like a "go forward"  situation since my Studio DAW seems to be working fine as-is, I can record and mix right now and it works perfectly, but it can't seem to digest the WAV files created on my other PA System PC. 
 
I think I'll hop on the PA System PC and export the tracks in a different format and then try importing those into my DAW. I might get that PC up to date with Windows Update first.  

Do you have Sonar on the other System? I record live shows to a laptop saved as Normal CWP projects to folders. 
I just transfer them over and open on my main DAW. 
 
The disk may be full is a common error. From the Knowledge base: 
 
If the disk space readout looks like you've got plenty of room, locate the file AUD.INI in the Cakewalk directory, and delete it. Next, go to Options | Global | Audio Data, and make sure the Data Directory is pointing to the proper path. If you've recently reinstalled or upgraded Cakewalk, this may be incorrect and you'll have to edit it now.