Are you in a mod development environment? If you are, you need to download BiomesOPlenty1.7.10-dev.jar so that gradle can compile it. If you are in a normal player environment, try downloading a different version for biomes-o-plenty or check if biomes-o-plenty has any core mods that you haven't installed.
YAS, adfly should be banned ofc, adfly may give developers money but is also known for GIVING PEOPLE VIRUSES, little kids get viruses on their computer all the time because of it. Adfly sucks and should be banned from planet minecraft
