If you're using the latest version of CCleaner, and it was the "Issues" feature of CCleaner you ran, try just running the "Clean" feature and see if that is problem free.
If this is the problem, you'd need to find out which removed registry key is causing the problem. Or, switch to another AV, and there are exellent free AV's available.
Or, stick with your current AV and avoid running the "Issues" feature until a fix is found for the CCleaner/PCGuard conflict. But if and when that will be I have no idea.