You can do it safelly with specific appz that are focused in deleting dead reg entries.

Also happened with me and it got solved.
Should consider saving the program in another folder..

Try searching for "registry cleaner" in any search engine.
Also try and check in the regedit what and wich file is runing the file that validates you Ableton: Usually it's like this:

HKEY_LOCAL_MACHINE\SOFTWARE\(THE FOLDER WHERE ABLETON IS SAVED)\ and then go to the root os the folder 2 check what's runing it...

ALSO SHOULD CHECK RUNDLL

It worked with me!