i wanted to report this bug

zoom in to see the picture better

As a suggestion, you can try checking only one item at a time in the tree and run the cleaning process manually until you get the error to show up.

While this won't solve the problem it will help people at Piriform to pin-point/narrow down what item is causing the issue.

While they don't fix this issue you simply keep the item unchecked and the error should not show up again.

I hope this helps!

...also make sure you have Administrator rights for your user profile. And what others have stated right click the CCleaner shortcut and select Run As, then choose Administrator.