As it stands users can only create threads in the buy or sell section but cannot respond to existing threads by other users. This was implemented to prevent bumping of threads and to avoid clutter. If you wish to contact someone for a purchase or they wish to contact you it has to be via private message through this boards contact system.
As for anyone else who encounters posting errors in certain sections. The staff do know about this issue and are attempting to address the problem at this time. The issue is on going and we are trying to find a fix.
"Its only a little bit on fire"