Ok guys, for everyone getting the error message, I found a way around it:
1) On the cruise planner select "Dining & Beverage" and then "All Dining"
2) Scroll down till you see "My Time Dining" options and the "View Details" button
3) Right click the "View Details" button and copy the link (in my case the link is "https://secure.royalcaribbean.com.br/cruiseplanner/category/1011/product/XXXXXXXXXXXXXX")
4) Change the link manually by inserting "/booking" before "/product (in my case it becomes "https://secure.royalcaribbean.com.br/cruiseplanner/category/1011/booking/product/XXXXXXXXXXXXXX")
5) copy and paste the new link and hit enter. You will be presented with MTD options.
Enjoy