Why can I not save?

[MR Flo-ax]

I just tried to save.

[Promidi]

Looks like a Windows permissions issue

Try running Cakewalk as administrator.... 

[Lord Tim]

It's likely you have some other process locking the file you're trying to save to, possibly an antivirus app (eg: Windows Defender) that's scanning the file at the time, or it's being indexed by a file sharing app like One Drive or Dropbox.

If you temporarily disable any of those things, can you save? If not, are you able to save to some other filename or location?

Expanding on what @Promidi said, it could also be a permissions issue. It's not a great idea to run Cakewalk as Admin, generally, but it's a useful troubleshooting step. If you are already running as admin, unless you have a really good reason to do that, don't. Run it as a regular user or you run into all kinds of wacky stuff like being unable to drag and drop things from File Explorer to Cakewalk, etc.

[Starship Krupa]

It's a good idea to go into the Windows Security settings and exclude your Cakewalk Projects folder from Defender's realtime scanning. Also your plug-ins and samples folders.

I don't think that's the issue, though. It looks like permissions to me. If you know how, check the permissions on your Cakewalk Projects folder to make sure that you have Full Control.