If a date is greyed out, it means that the doctor is not available on the given date.

If a time slot is greyed out and displays 'SORRY, SLOTS ARE FULL!', it implies that the doctor is fully booked for this time slot. Please select a different time slot to continue. 

Alternately you can try to book this time slot for a different day. 

Note: Please visit the clinic directly in the case of an emergency.