Voting for a witness not working

Hello @steemit, I am still a newbie here and maybe I am doing something wrong, but for some reason I am not able to vote for a witness.

I am having more than 30 votes which I don't know how to use. I followed all the steps:

I followed the link :

I get to this page:

Then, I have imported my account, clicked continue and I am getting this error message:

This was my fifth attempt. I tried to vote @brittandjosie for a witness also, just as I am trying to vote @arcange for a witness, and @steemitboard.

If any of you guys could help me get through this and explain what am I doing wrong, I would be very grateful