Bug: Error message for administrator accessing nonexistent account

If the administrator attempted to access (view) a nonexistent account, the application would exit with an error and yield a blank screen. With the original account manager, this could happen only if the user deleted the account between the time the list was displayed and when the administrator attempted access, but with the direct access facility, the error would occur whenever the administrator entered an invalid account. I added an explicit error message for this circumstance which includes the invalid account name.