While I was trying to vote up an asnwer I recieved the following message:
Come back to vote on more answers in X hours, or use your X remaining question votes now.
When does this message appear? And what does it mean exactly !
It means you can come back to vote on more answers in X hours, or you can vote on Y questions.
In other words, you've used up all of your votes for answers, and you still have Y votes left for questions.
Separate vote pools for questions and answers was implemented recently.
That mean, You can only vote on questions for today.
See Separate vote pools for questions and answers, which is newly implemented today.
You have 30 votes + 10 question votes / day now (previously there is only 30 votes limit)