Ok seems latest version has a bug under Windows 7
After updating the program as I normally would , just installing over the top
I get a dialog box..."Windows cannot find %Program Files%CCleaner\Cleaner.exe"

Now I tried uninstalling it and doing a clean install., same result.
So I jumped into the registry and it seems as if any registration of the application has had its keys deleted.
The Piriform Key was there but nothing else.
I uninstalled and put in the previous version and wallah no prob.
Welcome to the Forums.
Are you using x32 build or x64 build of Windows 7?
If you're using a x64 build it should probably install in Program Files(x86)
Run it as administrator, AND do a clean install.
And if after trying the above the problem still exists have a look at this thread with a similar problem:
http://forum.piriform.com/index.php?showtopic=28333
Thanks for the reply, It is 64 bit Win 7, and yes have done all that has been suggested.
Seems strange, doesn't matter what I try the same problem prevails. The latest version just fails full stop to install correctly
and I end up with that error message.
No probs I'll just leave it as it is on this version for now.