Thank you for reporting a bug in Linux Mint. Unfortunately I cannot reproduce your problem, so it's likely that you've changed something as root (using sudo) that has messed up your configuration. If you can reproduce the bug in a fresh install (probably a virtual machine, or a new user account) then please detail the steps necessary, including any extra software you added and all software versions. Please also check out the Linux Mint Forums, where there are many more people available to help out with diagnosing any problems you have. You might also like to check out this article: http://www.chiark.greenend.org.uk/~sgtatham/bugs.html
This is a standard response, so it may not be entirely appropriate.
I tried as many different ways I could think of to break it using multiple users (since this would seem to be a critical bug). On normal user accounts the authorisation understandably fails (though doesn't provide much useful feedback). On admin user accounts, the gui is closed on the other admin's account before being opened on the current, no conflict. Please provide a reproducable series of steps to trigger the issue.
If you have a question that has been answered and solved, then please edit your original post and put a [SOLVED] at the end of your subject header
Hint - use a google search including the search term site:forums.linuxmint.com