From time to time someone posts that CCleaner has stalled or frozen and won't continue.
I just saw it for the first time on a win 7 laptop from which I was removing the Vosteran search addon from Firefox and IE.
I used ADWCleaner. When it runs, it installs itself at C:\AdwCleaner, and anything it deletes goes to a "Quarantine" folder there.
At the end of the removal, I deleted the files at C:\AdwCleaner, then ran CCleaner to clear out the leftovers.
CCleaner stalled on that Quarantine folder in the recycle bin.
In fact there were 2 or 3 files in the recycle bin that had been deleted from Quarantine, CCleaner wouldn't delete any of them.
No processes were running that would have locked those files.
I think CCleaner won't delete any files that are in use. For example, I run Firefox Portable in a sandbox, and CCleaner won't touch it while it is running, but will delete everything when it isn't running. But CCleaner doesn't stall in that case, it just leaves the active files untouched.
As a solution, I just restored the quarantined files to their original location, used CCleaner to delete what was left in the recycle bin (this part worked fine), then deleted the quarantined files again, opened the recycle bin, and deleted them directly from there. Worked OK.
And the point, for any who may still be awake: Those quarantined files must have had some special attribute that stopped CCleaner, but not normal deleting. It would be nice if there was some way for CCleaner to notify the user why it has stopped.