No, this does not appear to be an activation issue.
 
Are you running 64bit Windows?
If so, does the SONAR About page have "x64" at the end of the version?

@chuckebaby: Thank you. You're right, of course.

@scook: I am running 64-bit Windows (10, Creator's Update, 1703), but I could never get the 64-bit version of Cakewalk to run on this machine, starting with Windows 7. It just always crashed on startup. So I'm running the 32-bit version of Cakewalk. The Start Page ran fine on Sonar on Friday night. As of last night, it didn't. As far as I know, my computer hasn't changed. I've been on the Creator's Update since June.

@bitflipper: Help -> About says 21.7.00 BUILD 18 Hopkinton. Command Center says 2016.08 (22.8.0.030).

OK, here is what is happening. By default, the Command Center updates the version of SONAR based on the OS. This means you have been updating the 64bit version of SONAR. In this case, the update indicators only apply to the 64bit SONAR.  IOW, the version of SONAR you are actually using has never been updated. To update the 32bit version of SONAR from the Command Center

• run the Command Center
• click the Gear in the upper right to access the Setup screen
• check the "Verbose Install" option
• click Save

Now when you run the SONAR installers you will have all the prompts as if you ran the installers at the command line. One of the prompts is the 32/64 option.
 
It is possible to run the installers directly from the Command Center download area and forget about the Command Center. By default the path is "C:\ProgramData\Cakewalk\Command Center\Downloads." The actual path is in the Paths tab in the Command Center setup screen. This will show all the prompts too (regardless of the Command Center settings).
 
You will need to re-run the installers to get the 32bit update. All updates are cumulative so you will only need to run the last the most recent version of each installer.
 
If you want to work the crash issue, create a separate thread.
 
 
 
 

OK, if I launch Sonar from the link in Command Center, it runs the latest build, 22.8.0 BUILD 30 [2016.08] - x64, the 64-bit version (which, by the way, seems to be stable). If I launch Sonar from the icon on my desktop, it runs the 32-bit version. Maybe best bet is to uninstall and start fresh.
 
@scook: Update, I just saw your latest reply and understand now what's going on. If the 64-bit version runs OK now, maybe I can use it instead. Thank you for your help and in steering me in the right direction.
 
 

That would be an option. The clean install instructions are here
Again, you only need to run the most recent version of each installer.

Another thing that I've seen happen is that links are sometimes not updated as expected on the start page or the taskbar. What I have done is delete those links from the start page and the taskbar, re-add them, and then they will reference the newest version. This has worked for me multiple times.

Good call, Steve!
 

One of the best help threads I've seen!