I would try a different browser or use your phone...
Seems to work just fine.
Edit:
Wait, is it because you're trying to use PayPal and the option is greyed out? TRU doesn't like to use PayPal for pre-orders but is IS possible and they do allow it. You use the regular checkout method and switch to PayPal on the following page. They deduct the $ and then put it back in your account until the item ships... it's like a 10 day process but they do it to ensure the funds are in your account at the time of order. The PayPal invoice will state Pending until the item ships and the funds will be deducted once again from your account.
