Nevermind.  Turns out the thread I was trying to reply to was locked and I didn't notice because the icon didn't draw me to it.  Perhaps removing the “reply” link from locked threads (or putting “thread is locked” somewhere) would be a good UI improvement to these boards?
Also there is no mouseover popup to explain icons, nor is there an icon legend anywhere (as far as I can see; although I haven't looked very hard) to explain what the icons mean.  Can we get something like that?
                    
                    
                        
Edited Lyle Waldman (Dec. 13, 2012 07:08:12 AM)