CCleaner periodically pops a dialog stating:
An error has occurred in the script on this page
Line: 666
Could you give more details?
Is this Windows, Android, Mac?
TBH that sounds more like a browser message. is this the CCleaner browser?
Have a read here also for clues. According to that thread someone got the 666 line error in September (a few weeks ago)
https://community.ccleaner.com/topic/55627-script-error/