This just happened to me. Turn 5, Unable to use my reinforcement card (When I selected reinforcement, it would highlight 5/6's of a priority card instead. Exactly what Rikku described.
last card on the right, non whole card.). I refreshed, signed out and back in, Still unable to use it on turn 6. Then on turn 7 I was able to use the reinforcement card. and everything proceeded normally, until turn 10 when I was unable to use a delay card. (Same deal. it highlighted last non-whole card on the right instead). Turn 12 unable to use blockade.
I still won the game :) It presented a new sort of challenge.https://www.warlight.net/MultiPlayer?GameID=13397324