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Hmm i just got that error when trying to post a comment

Transaction failed: trx.ref_block_prefix == tapos_block_summary.block_id._hash[1]:

It appears to be when you were on the blog submit screen too long - perhaps you left it up coming back several hours/days later. I believe that it is due to a module of Steemit timing out after so much time has passed. Copy your text, refresh page or even re-navigate to the page and then you should be able to post without this error. If that fails, logout and log back in which should ultimately fix it.