Solved "security client user interface has stopped working" message in Guest user account.

Hi, I have two user accounts used by my wife and myself and Microsoft Security Essentials (MSE) works fine on both user accounts. Very occasionally our daughters visit and use our pc. They use the Guest account. I just happened to log into the Guest account and got a pop up message saying that Microsoft Security Client User Interface has stopped working. When I closed the message I noticed that the MSE icon was missing from the Notification Area. When I tried to open MSE from the Start Menu I just got the pop up message again and MSE would not open.

I would add that I have no other anti-virus software running on my pc apart from MSE.

I would appreciate any help that anyone could give me