Lately I can't seem to choose certain cards to play. I can hit End Round and it will let me play the card the next round, but I can't play it that round. This is just starting to happen, and I'm around Level 11 or 12.
I don't remember them having halt or stun cards, so we may have a bug here, but it never really happened to me nor I've seen it on the forums. Maybe there were zombies on the map - with "brains" card?
Do you have any cards attached to that character? Examples of cards that you inflict upon yourself: fright, trip, squeamish, hit the deck.
No, I don't think I had any of those attached. Also, when I am in the character screens, sometimes I can't select any of the items they have equipped. The only way I can see the detail of their equipped items is if I select a non-equipped item and drag it over to compare. I think it's kind of buggy in general this way - where things that I normally can select just fine won't select. Mind you - I can select some cards on a character in battle while not being able to select others (even same types of cards, like attack cards).
Also posting general info like what Operating System you're using, the Browser you play CH with, if you're playing on Kongregate or the main site, etc. That can help with this sort of issue.