From this thread, looks like those error codes are because you have no STEEM Power.

You have to "Power Up Steem" from your wallet.

There might be a way to earn curation rewards by posting replies / comments.

Another question to those with the original errors: you can post comments and replies. How about actual posts?

The STEEM blockchain runs every 3 seconds, so sometimes it is a timing issue:

I even got error code

RPCError: Assert Exception:( now - voter.last_vote_time ).to_seconds() >= STEEM_MIN_VOTE_INTERVAL_SEC: Can only vote once every 3 seconds.

when tupvoting all of you too fast!