Can't install programs and unlock settings

Hi all!

I'm currently experiencing a strange behavior: When trying to install a program everything works normal until I get to the (admin) password prompt. After typing in the password and pressing return, the password prompt closes but the installation just doesn't start. Nothing happens, not matter what app I am trying to install.

The log states the following:

04.10.15 13:27:38,314 authorizationhost[1895]: {processRequestCreate} Failed to create agent mechanism, failing authentication!

04.10.15 13:27:38,314 authd[142]: engine[2324]: error creating mechanism agent

04.10.15 13:27:38,314 authd[142]: engine[2324]: evaluate returned -60008 returning errAuthorizationInternal

In parallel I have another problem that is apparently linked to the first: When I try to unlock system preferences (for instance the "security" settings) the prompt appears, my password is accepted/prompt closes but the settings are still locked.

The log states the following:

04.10.15 13:31:46,014 com.apple.preference.security.remoteservice[2353]: Unknown class AddRemoveBarCell in Interface Builder file at path /System/Library/PreferencePanes/Security.prefPane/Contents/Resources/Base.lproj /SecurityPref.nib.

04.10.15 13:31:46,266 com.apple.preference.security.remoteservice[2353]: AutoSubmitPreference is 0

04.10.15 13:31:55,917 authorizationhost[1895]: {processRequestCreate} Failed to create agent mechanism, failing authentication!

04.10.15 13:31:55,917 authd[142]: engine[2353]: error creating mechanism agent

04.10.15 13:31:55,917 authd[142]: engine[2353]: evaluate returned -60008 returning errAuthorizationInternal

As I am currently not able to create a second admin account (I only have one account on the machine) via the settings panel I created a password for the root user via the terminal. Surprisingly everything works when using that account.

Other things I have tried so far:

- repairing disk permissions & key chain

- using root credentials in the affected profile (didn't work)

Does anyone have an idea how to solve the issue(s)?

Thanks!