This could be due to a few reasons:
- The member's membership type is not included in the active booking rules.
- The member has not registered for online booking.
- The casual booking rules are set to "View" instead of "Book".
- Members are not allowed to book the Reservation Type*.
To edit Casual Booking Rules go to "Tools", scroll down to the "Members Booking" section and click on "Casual Booking Rules". Select the 
icon on the right hand side of the rule you want to edit.
*Providing that the casual booking rules are active, members can only make casual bookings when the Reservation Type is set to "Members", "Reserved for Members" or if the tee time is completely empty. (Reservation Types can not be added to this list)
You can edit their ability to book "Reserved for Members" and completely free tee times in "Tools" >> "System Configuration".