I have recently discovered that use of the utility application “Clean My Mac” can break CS5’s ability to update itself. Clean My Mac, in it’s default setting, will remove international language files from applications to recover the “wasted” disk space. In most cases, this is action is harmless to the operation of your Mac. However, if you have Adobe CS5 installed (any flavor), the Adobe Updater looks for the language files to update them and bombs out.
The fix is to reinstall Adobe CS5 and reapply all patches. You can simply run the installer on the main disc without first uninstalling/unregistering the existing install. The Installer will overwrite the files and update all plists. The launch the Adobe Updater from within any app in the set and then exit the app to allow the Updater to do it’s job unimpeded. Please make sure all browsers are closed when this action is taking place.