Disabled Sessions should be joined - DisabledSessions
The whole string, if you want to paste, is
reg delete HKLM\SOFTWARE\Microsoft\SQMClient\Windows\DisabledSessions /va /f
The "r" is not needed at the end.
P.S. Sorry. I am having some problems with the post. I can see that the two words still appear to be separate.. They must be joined.
If you don't want to type it all out , copy and paste into notepad and join the two words, then copy and paste back into the Command window.