All of my VDB vouchers are not "clickable" when I try to book via the delta.com. I have had to call each time to redeem with an agent - no charge of course due to .com issues. I did get a chuckle from the agent when I booked my bos-msp-sju-jfk-msp-oma miles run a few weeks ago

The only vouchers in the last couple of years that I have been able to use online are those generated when selected as my platinum/diamond awards.