Failure to adjust clock on startup

Ubuntu is able to detect if the computer clock is set wrongly on startup, at least if the time has been set back. A dialog will appear, saying something like "The computer clock appears to be wrong", and you get two options, "Ignore" or "Adjust the Clock". This dialog appears after entering username and password.

If I choose "Adjust the clock", an error box appears with the message "The configuration could not be loaded. You are not allowed to access the system configuration".

Unfortunately this also causes the startup to hang completely.