There are two reply options. One is normal and one is quick reply. Quick reply hasn't worked properly for months. Unsure how to fix. The main reply should not show the invalid session message.
aaah right, sorry about that, I never normally use it but I've started using it on another (wedding) forum so think maybe I'm just used to it and might have been doing it here too! OOPS!
its cool, it cant happen anymore, i didnt know whats wrong with it, so i've simply deleted the button from the topic viewer pages, so its like its not there anymore.