cannot close the application

When I have chrome open and start the cleaning, I get teh message "cannot close THE application". I closed chrome and the message remains.

also the message is unclear, what is THE program? better would be replaceing THe with the real application name.

also: when the application is closed, stop the message from popping up, now I don't know if THE app is chrome or another app I have running

Chrome can/will run background processess even when it is closed, and it's those background processes that can prevent CCleaner from cleaning it.

But it does usually tell you that it's Chrome and not just 'The application', so as you say it may be some other app.

One step at a time, let's rule out Chrome first:

See this article on how to stop Chrome running background processes when it's not open:

https://support.piriform.com/hc/en-us/articles/204210674-Why-is-Chrome-cleaning-being-skipped-#why-is-chrome-cleaning-being-skipped–0-0

PS. Please tell us which Windows version you are using (eg. Win 10 20H2), which CCleaner version, and which antivirus you are running if it's not Windows Defender.