Hey there, Michelle, and welcome to planDisney! We're so glad you stopped by with your question.
It looks like I'm answering one day after the arrival date you indicated when submitting your question. I'm hoping you were able to get your question resolved, or at least that I can still help!
Though I don't know the specific details of your tickets, I have seen some tickets that are only eligible to be used on certain days (like only on weekdays, for example). I'm not sure what days you were trying to reserve, but it's possible that your third day was falling on a day that was ineligible for your particular tickets.
If you haven't done so already, my recommendation would be to
call a Cast Member at the Tickets line or visit one of the ticket booths at the Disneyland Resort if you're already there. They should be able to help you figure out what is going on. If it turns out to be a technical glitch, then I'm hoping they can also help you sort out a solution for your third day!
Since it looks like you might be visiting the parks right now, I would highly recommend making time for the new nighttime spectaculars -
Wondrous Journeys and
World of Color - ONE. They are unbelievably magical! Also, make sure to catch a ride on
Soarin' Over California while it's there for a limited time as part of the
Disney California Adventure Food & Wine Festival. I absolutely love this iteration of the attraction. Nothing beats the scents while flying through rivers amidst the pines and over the orange groves - just watch out for flying golf balls!
Thank you again for your question, Michelle. I hope you have such a great time at the Happiest Place on Earth!
Have a Magical Day,
Greg