could be different reasons for this, but main one is usually post age - anything older than 7 days can't get more votes and the tokens from that post are distributed to poster and 'curators' (a half advanced topic you can safely ignore around here), so on voters end it will look like the vote button is kinda broken, but that is from steem blockchain refusing any change in payout on the old blocks, basically.

the second reason is RC 'Resource Credits' which you can check here: https://steemworld.org/@celticdragon

there you will see your current vote mana %, vote power at that % (rounded), and many other things. It looks like maybe you're a bit low on RC, which is based on steem power. The general idea is to not have brand new accounts suddenly join and go into spamfest mode, but the downside is legitimate users can also be restricted. Your RC will regenerate over time the same as vote power, so it is a kind of throttle. A long time ago I made a guide about this, that is still mostly relevant: how-to-avoid-the-bandwidth-limitation-problem