This happened to my Mom when she tried to use a DBCFree voucher. She mailed the voucher to the United Customer Service Center two weeks before flying, per the usual instructions. Unfortunately, it didn't clear the CSC process in time, so her flights were canceled. She didn't discover this until she arrived at the airport. There were many tears, but United wouldn't budge. I ended up booking an award ticket for her for the next day.

ballsandboards is it possible this situation could have occurred? Did you receive any confirmation that the ticket was finalized in United's reservations system? Were you able to see it in your My Itineraries list?

Edited to add: If it's still more than two hours before flight time, is it possible for ballsandboards to purchase an award ticket? The application of 25k miles might solve his problem.