Message headaches

Does anyone else have issues with TN Message codes? Despite checking once, twice, three times that I have entered the code correctly before hitting the send message button, 9 times out of 10 the site tells me the security code does not match. Worse still you lose the message text and have to re-type it. I've taken to copying the text before hitting send so I can at least paste it in and resend. The resend then works every time. Driving me mad. Am I being stupid or is this a known problem?