I can't help you with why you are getting that error message, however
the best way to create a switchboard is to avoid the built-in
switchboard manager completely.
Create your own switchboard using an unbound form with command
buttons. If you use the command button wizard to add the buttons
Access will write most of the code for you. You will have more control
over it's appearance, won't be restricted to 8 buttons, and
maintenance will be much easier. Try it.