I hope I don't ignite anger inside some RuneMaters for bumping an old ass thread.
However, I had this problem for over a month and just got back into my account so thought I'd post a reply. I found this thread while googling the error.
The problem was the time on my phone was 2 minutes slow... for some reason automatically update date and time was turned off (I'm pretty sure I didn't turn it off) but anyway I flicked it back on and my authentication code was working again.