Had you been voting a LOT prior to this?
Looks like your voting power may have dropped too low. You can check it by clicking here and checking the 'voting power' line. The more you vote the lower your power drops. But it does recover. Looks like your back at 86% now. So you can try again. If its not that it may have just been a bug in the transaction. You can just try refreshing the page or signing out/in again. Good luck.