If it has been more than 20 minutes and your progress bar has not finished loading to 100%, it's a good idea to rebuild that Media Center.
If you look to the right of the progress bar, you'll see an X (to delete), and next to that, two arrows following each other in a circle. Click those arrows, select "yes" on the popup, and it will rebuild your Media Center. If it's still sticking after another 20 minutes, please send in a support ticket.
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