I feel your pain!
TRy to book again. Take a screen shot of each page during the booking process, then call a FB Call Center Supervisor to explain that it was a technical issue , not an award availability issue, and the Sup should be able to manually book your ticket by booking a REGULAR award ticket, then doing a manual recredit of miles for the 50% discount. Convoluted...I'm afraid so, but it will accomplish your goals.