I had the same problem and it is something with either java or flash.
I switched from chrome to internet explorer and could type in the forum for about a day. Then same thing ads blocking the reply box.
got a poper blocker, javascript popup blocker, flashcontrol,Avira browser safety, and adblock plus...One of those took care of it and the only downside so far is my yahoo mail page looks dimm, but all is there and usable on it... I fought this for 2 months.
It affected all forums that I went on , not just this one.