Probably just a glitch. You will have to wait till the next time you can vote and hopefully it will work.
this has been happening to me too, it started after my name change, i think it's broken.. really needs to get fixed
Unfortunately, this has been happening to many players. The system may be glitched (most likely), I hope we could find a way to fix this!
A lot of players have been coming to me for help with this situation, I hope it can be fixed. Fortunately, I am not dealing with this issue.
