User Accounts window opens when clicking on the Start button

I have been using Vista for about 3 months now. I have the task bar located
on the right hand side of my screen. Within the last few weeks every time
that I click on the Start button, the User Accounts window will open. This
just started within the last few weeks.

I know that if I put the task bar back to the bottom of the screen this does
not happen. When the task bar is located on the right hand side, the User's
picture is located right over the Start button. Also, if the task bar is on
the right hand side and you make the task bar wider so that the User's
picture is not located over the start button when clicked then you do not
have the User Accounts window opening unexpectedly problem.

Does anyone know if there is a fix for this or if Microsoft had an update to
fix something else but had this unexpected consequence? I would be happy to
remove the update.

Thank you very much for your time.