There are 2 registry keys that CCleaner wants to delete, but I haven't let it because I'm not sure what these keys are exactly.

* Unused File Extension: WMPCD - HKCR\WMPCD (Do I want this removed? I'm guessing that it's associated with Windows Media Player.

* Unused File Extension: .dmg - HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.dmg (I don't have any idea what this is, but I will do some investigating.)

I also got the following error a few times, but now it seems to have stopped. I don't know why it stopped.?
* Software\Microsoft\Windows\CurrentVersion\AppManagement\ARPCache\KB912919 could not be located. I don't know what I did or didn't do to cause or stop this error. Any ideas?

Thank you!
K

* WMPCD is a Windows Media Player protocol that enables you to specify tracks on a compact disc using URL syntax. I will keep this.

* .dmg is the file extension for the Macintosh disk image file. I don't have any idea why this is on my computer...Windows can't use this right?

Unsed file extensions get regenerated when a file is created with an extension that dows not have a registry entry so deleting the *.dmg is quite safe

Just back them up when you delete them and you can always restore them if deleting them creates a problem. Annie Brion is correct, though, deleting unused file extensions is not going to cause problems.

CCleaner identifies that issue on my computer intermittently. ARP (Address Resolution Protocol) Cache entries are automatically created and deleted when required during network TCP/IP sessions. I've always assumed CCleaner is finding a reference to a deleted entry. You can fix them or ignore them ... the cache size appears to be very limited so they don't seem to accumulate to any significant size.