Crashing for client

So, today I wanted to go on 1.7.10, each time I try to go onto a server ect I crash. It says my game is modded, modded type is client. If it helps, I got Minecraft when 1.8.1 was the latest version on January 31st. This would of been my first time playing on 1.7.10 but since It keeps crashing I can't. I wanted to use 1.7.10 since I got the mod Biomes O' Plenty. I've been trying for a while now, and I keep crashing. I would appreciate help as I was so excited to play with biomes O' plenty.