Hi Folks, A while back, I upgraded my Mac OS X Leopard to Snow Leopard and encountered some strange behavior which did not allow me to authenticate anymore. This lead to very ugly situations where no software could be installed anymore (since the dialog didn’t fire up to enter the password) and some settings could not be changed. Some installs later, I figured it was a Problem with the alternative keyboard layout I’m using. This particular layout has been put together by Jan & Nils [1] and puts the German Umlauts on some of the keys by utilizing the option key. The problem arose when the alternative German Umlaut keyboard Layout had been installed. For a solution see the entire article. So I scanned through the logs and found this essentially: windowserver.log ------ Sep 11 17:26:17 [317] kCGErrorIllegalArgument: CGXSetWindowFilter: Invalid filter 2 Sep 11 17:26:17 [317] kCGErrorIllegalArgument: CGXReleaseCIFilter: Invalid filter 2 system.log ------ Sep 11 17:27:47 H9s-MacBook-Pro SecurityAgent[709]: CFDictionarySetValue(): immutable collection 0x100114b40 given to mutating function Sep 11 17:27:47 H9s-MacBook-Pro SecurityAgent[709]: NSExceptionHandler has recorded the following exception:\nNSUncaughtSystemExceptionException -- Uncaught system exception: signal 5\nStack trace: 0x7fff824482d3 0x7fff874850aa 0x158 0x7fff83b38ab7 0x7fff849f2d7c 0x7fff849cff0d 0x7fff849cf58b 0x7fff849cee79 0x7fff849d6db0 0x7fff849d6b28 0x7fff849c85a1 0x7fff849c805b 0x7fff849c7b31 0x7fff849c79b1 0x7fff849c790c 0x7fff82c19520 0x7fff82c18e89 0x7fff82bdea7d 0x1000020ae 0x100001f58 0x1 Sep 11 17:27:47 H9s-MacBook-Pro SecurityAgent[710]: CFDictionarySetValue(): immutable collection 0x100407b00 given to mutating function Sep 11 17:27:47 H9s-MacBook-Pro SecurityAgent[710]: NSExceptionHandler has recorded the following exception:\nNSUncaughtSystemExceptionException -- Uncaught system exception: signal 5\nStack trace: 0x7fff824482d3 0x7fff874850aa 0x158 0x7fff83b38ab7 0x7fff849f2d7c 0x7fff849cff0d 0x7fff849cf58b 0x7fff849cee79 0x7fff849d6db0 0x7fff849d6b28 0x7fff849c85a1 0x7fff849c805b 0x7fff849c7b31 0x7fff849c79b1 0x7fff849c790c 0x7fff82c19520 0x7fff82c18e89 0x7fff82bdea7d 0x1000020ae 0x100001f58 0x1 Soo after that, I figured out this possible but very ugly Solution: rm /Users/username/Library/Preferences/ByHost/com.apple.HIToolbox.SomeUUIDhere.plist But now I found a better and finally working solution: Put your alternative layout (in my case called roman.bundle) in /Library/Keyboard Layouts/ and not in /Users/username/Library/Keyboard Layouts/. Meaning: make the layout available to all users. Hope this helps someone. Cheers [1] http://hci.rwth-aachen.de/USGermanKeyboard