Just a further update on this. When I launch Ccleaner I now get a Crash Report coming up saying "The application Ccleaner has quit unexpectedly" and asks me to send a report, which I've done. However, if I simply press the cancel button on the crash report, Ccleaner then runs as expected. Very strange! Not sure why it gives this crash report then runs when cancelled. There must be a bug somewhere in the system but at least I can get it to work.