An athlete will not be able to sign into a class until the WOD has been made public. If an Admin has not set the WOD to be public or simply did not create a WOD for a given program, sign-ins cannot occur.
In cases like these, a WOD will simply need to be programmed to utilize early sign-ins. Another option would be to enable reservations. Reservations will allow your athletes to claim their spot in class regardless of whether or not a WOD has been programmed.