Lux E bug in ARAM

Today I got Lux in ARAM and everything was fine until I maxed my E with 5 points. Then the icon went dim and whenever I pressed E, I got the "You cannot cast at this time" message, as if it was on cool down. I left the game and rejoined, hoping to fix the problem, but it was still disabled. I had played a few games on Summoner's Rift as Lux just a few minutes prior and did not have a problem.