Yesterday, when I tried to upvote a post, I got an error:
I thought it might be a glitch; but today it persists.
@guilhem: do you know why is it so? Besides having rather advanced TL, which should provide rather substantial number of available votes, I am also sure to not vote much at all 
Reading the source, it seems I misunderstood the implication of leaving qa_trust_level_vote_limits disabled: it prevents upvoting multiple times in a given topic. Enabling the features gives per-TL maxima, currently 1, 2, 3, and 4 respectively for TL1, TL2, TL3 and TL4. (That’s just the default, we can adjust if needs be. But should be able to upvote another post in that topic now :-))
