According to AskBA

"There are certain routes (due to immigration security reasons) where online check-in is not available. They currently include:
Kano Lagos Abidjan
Abuja Almaty Belgrade
Bologna Brisbane
Cancun Dhaka Dar Es Salaam
Gdansk Genoa Helsinki
Islamabad Kuwait
St. Petersburg Ljubliana Mauritius
Naples Pisa Riyadh
Seychelles Skopje Sofia
Moscow Salzburg Tobago
Tehran Venice Verona
Zagreb Eindhoven Rotterdam
Aleppo Alexandria Amman
Baku Damascus Yerevan
Bishkek Luxemburg Tbilisi
Dublin Liverpool Knock
Shannon Waterford Alicante
Casablanca Faro Funchal
Murcia Malta Palma"