Clean My Mac X " can't be opened. What happened?

There is no reason to ever run any "cleaning", "optimizing", "speed-up" or anti-virus apps on your Mac.  This user tip describes what you need to know and do to protect your Mac: Effective defenses against malware and other threats - Apple Community. 

Also uninstall Avast. That also was probably a major contributor to your Mac's lack of performance.

Uninstall both according to the developer's instructions. When done you can check to see if you've removed all of the files by downloading and running the shareware app Find Any File to search for any files with the application's name  and the developer's name in the file name.  For example for these two apps you'd do the following searches: 

1 - Name contains clenamymac

2 - Name contains macpaw

3 - Name contains avast

Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion.

FAF can search areas that Spotlight can't like invisible folders, system folders and packages.  

Uninstall CleanMyMac per their directions , Restart then run etrecheck again to see what chaff it left.

On CMM…

https://discussions.apple.com/thread/251370955?answerId=252661013022#252661013022

https://discussions.apple.com/thread/251442443?answerId=252814053022#252814053022

https://discussions.apple.com/thread/251464557?answerId=252841819022#252841819022

To answer your original question without commenting on the value or worth of CleanMyMac, it is likely that Avast suspected a critical file associated with CleanMyMac of being malware. When it does this, it moves the file to the Avast virus chest. This is most likely the reason why CleanMyMac won't run.

If you want to continue using CleanMyMac, then go to Avast, click on the Virus Chest, and restore the CleanMyMac file to its original location. Once you do that, it will run again.

I hope that helps.

Read thru the multiple answers and with all due respect to those who are trashing CMMX they are welcome to their opinion and while I respect it, they are wrong. I have used this program for a number of years and find it very useful. Yes there is an issue w/ it and Avast - open Avast go to virus vault, check the CMM file there, and restore. All works for both CMMX and Avast. Now one place that I totally agree w/ many, Google Chrome is a pile of junk and as soon as Avast installed it I uninstalled it. As to those who don't seem to think Macs need AV protection or that Macs "clean themselves" - wrong. ANY operating system can become loaded down and need an occasional cleaning and CMMX works well for that in my opinion. Also more and more as usage of Macs increase hackers are beginning to attack and infect w/ viruses & malware so beware!

Please do and also PLEASE uninstall the the third party antivirus app per the developers instructions. Adding CMM and third party AV apps add zero additional layers of security to Mac OS. If simply kept up to date and otherwise left alone Mac OS runs very stable and secure for most users. When users introduce third party AV and cleaning apps, they cause Mac OS to be slow and appear to have bugs. The best cleaning and AV app for Mac OS is Mac OS itself.

CleanMyMac is complete garbage. It will do more to harm your system than it will to help it. Remove it. And while you're at it, remove the antivirus software. It is also completely useless on a Mac.

One more thing, is Google Chrome to be trusted? I read that the program was imbedding itself deep into hard drives.

Yes it does. It's important to understand Google is not just a browser. It's a pervasive system modification specifically designed to turn your Mac into an information-harvesting and -uploading "bot". That is its sole reason for existing. It also updates itself automatically, meaning a Mac that runs well one day might exhibit the symptoms you describe the next day, even if you changed nothing about it or what you do with it. In fact, it was one of those updates a while ago that caused Macs to crash and become unbootable, for which the only solution was to reinstall macOS. Oops!

Google is the closest thing to a Mac "virus" there is, or has ever been.

Brave doesn't do those things. Neither does Firefox, nor does Opera. Only Google Chrome does it. And as browsers go, it's not a very good one anyway, which holds true for Macs as well as Windows PCs.

Plenty of people use Chrome and like it. Ok for them, but it's incumbent upon everyone to educate themselves regarding its purpose and its implications for privacy and data security. Google is not your friend.

And while we're on that subject: Avast has had some practices that surprised some users of the product (hat tip to MrHoffman).

Google is noted for mining info about the user on the computer where its software is installed. It's also a resource hog. If you need a browser other than Safari give Firefox a try. It's much more secure than Chrome.

David Bernstein1 wrote:

I neither encouraged nor discouraged any practice. I simply answered the question of the original person who posted. That, after all, is the purpose of these forums.

The purpose of these communities is to help other users. Advising them to use third party apps such as AVAST and/or CleanMyMac is not helpful, in my opinion. Search these communities to find the thousands of posts where these and similar third party apps have caused issues.

The OP came here for an answer to his question. I provided that. I did not advise anyone to use CleanMyMac, Avast, or any other similar third party app. I merely provided the correct and accurate information in response to OP's query, pointing out that I was not commenting on the worth or value of Avast or CleanMyMac.

You will also find that I am neither lauding nor criticizing your responses, so perhaps you could return me the same courtesy.

David Bernstein1 wrote:

The OP came here for an answer to his question. I provided that. I did not advise anyone to use CleanMyMac, Avast, or any other similar third party app. I merely provided the correct and accurate information in response to OP's query, pointing out that I was not commenting on the worth or value of Avast or CleanMyMac.

You answered the question but didn't address the actual problem. The OP's Mac was overworking, running slowly. Getting CMM to launch wouldn't solve that problem. Sometimes, especially with people who are less experienced, they don't know what questions to ask or where the problem lies. One needs to take the larger context into consideration.

Our role here is also to help guide unsuspecting users around known pitfalls, like Avast and CleanMyMac, based on our experiences here in the ASC. Advising them to avoid known "bad actors" is part of our responsibility.