If a message doesn't "take," it's gone forever. Usually, what happens is that you've posted on a thread that was stored on your computer, not loaded fresh. As a precaution, it's best to highlight [CTRL-A] and copy [CTRL-C] all long messages before you post, and then check the thread to make sure it posted. If it didn't, refresh [F5] your thread to make sure it's a new load, and then paste [CTRL-V] your message text into a message box and "Submit."