What in the world am I doing wrong? No matter what I do I still receive this message. I've copied and pasted, retyped, assured I'm doing it as Admin... what else could it be?
One issue that has been noticed with the new registration box is if you have a space(s) before or after the key when you copy/paste it then it won't be recognised.
A fix is being worked on.
If copy/pasting then make sure that you have no whitespace before or after the key.
If typing it in then be careful not to confuse numbers and letters, eg. S and 5 can be mistaken.
And just to make sure, the '-'s are needed in the new box.
PS. Is this for a Mac computer? (your previous post was about a Mac).
If you are using a Mac then it's best to post your topics in the 'CCleaner for Mac' forum so that people are aware of that.