Hello and welcome to planDisney, Nozomi (Youkoso!). Thanks for bringing this question to us. I'm so excited about your upcoming visit to the Disneyland Resort and I'm thrilled to help.
As Timon and Pumbaa say, "Hakuna Matata!" It means no worries (shinpai shinai de) and I'm not the least bit worried about your theme park reservation, so let's take a look. It sounds like you might be receiving this error message because you may already have a theme park reservation.
You can visit the Disneyland site and log into your Disney account and click on "My Plans" which can be found under the heading "My Disneyland" towards the top right. Here you will see a list of all of your valid theme park reservations. If you don't see your reservation listed here, you can visit a
local travel agent for help with securing one.
Once you have your theme park reservation you'll be all set for your visit to the Happiest Place on Earth. There are so many wonderful things happening at the Disneyland Resort like the
Disney100 Celebration. You'll see the resort decorated in beautiful purple and platinum decorations and there are also two new nighttime spectaculars to experience. I love
Wondrous Journeys - there's nothing quite like seeing Baymax soar over Sleeping Beauty Castle.
Speaking of Baymax, the Pacific Wharf in Disney California Adventure Park is currently being transformed into
San Fransokyo Square. This newly reimagined area is scheduled to open later this summer and I hope you are able to visit during your magical stay.
I hope this has been helpful, Nozomi. Please come back to visit us with any other questions that you may think of. Here's wishing you a most magical visit!
Mata aimashou,
Michelle