When you try to delete a user from the security UserAdmin form, you receive the following error:

System.ArgumentOutOfRangeException: 'lstUsers' has a SelectedValue which is invalid because it does not exist in the list of items.

This apparently refers to the user that was deleted because after going back and checking the form, the user was deleted successfully.

Also, when you are in security administration mode and you open the Control Security Configuration dialog, you cannot close the dialog using the close button without generating the following error:

Microsoft JScript runtime error: Object expected
at Line 134: onclick="CloseWindow();

You can , however, close the window from the X box at the top of the form.