I have tried several iterations of the rule, including the simplified switch rule such as the one you suggested, but I still get the same error, "Function does not return a value."
I have double-checked the names of the pages and they do match what is in my rule.
It is a Callback rule – an OnRecord Start rule.
I have tried writing a rule to do the opposite, to initially have all my pages set to "Used" and then have the rule turn off all the unwanted pages. That rule does not give me an error message, but is a very long and cumbersome rule. It is almost like the program wants to have at least one page initially set to "Used" under Manage Pages. And as I said before, it WORKS, but it gives me an error message anyway. I hate to just ignore the message, but I'm not sure what is causing it.