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Generally speaking that message indicates that LV has not figured out what to do with all of the possible values that can be passed to a case structure. This is not the case in the VI you posted.
Please recheck what you posted and reply with more info if you still need help.
The VI you posted has no error. If you have a case structure wired to a Boolean, you must have both a true and false case defined. If you have a case structure with a numeric, string, or enum wired to the selector, one of the cases must be defined as a default case. To make a case default, right click on the selector level and select "Make This the Default Case". A default case is necessary to handle any unexpected values.