Still investigating, but it appears I ran out of steem power.
As of an update in 8/2016, SteemIt implemented these two rules:
1 - minimal rshares per vote will now be enforced
This effectively stops accounts with really low amounts of steem power from voting. Preventing spam of meaningless votes. This update was made with the intention of preventing bot attacks.
2 - new proof of work algorithm that prevents short cut calculations
After the recent mining attack by a user named 'supercomputer' the steemit devs have been working hard to fix this bug. 'Supercomputer' did this attack by skipping the hashing part of mining and using ECDSA instead. The hacker could submit new blocks, using old blocks and changing their block-id. Then change his private key to sign the new block, effictively skipping the POW. @arhag will soon fully disclose how all of this took place.
Sounds like 20-30 upvotes per day until you gain enough reputation to muster more...
Here is what the message looks like:
that's interesting to know :)