Join Date: Nov 2018
Location: Istanbul, Turkey
Programs: TK Elite Plus,BAEC GGL,ITA Executive, AFKL Gold,QR Gold,HH Diamond,Bonvoy Gold,ALL Gold
Posts: 14,186
If the flight is overbooked on a certain cabin ( in your case Business ), they would disable online check-in and seat selection over there. This is standard practice by TK.
I would suggest going to the airport early, especially if you are not traveling alone.