Yea, and I guess all those other people who all have this same error are very likely also using a cracked client.
To make it clear : even I just don't want to ... I even CAN'T cause the "hacker" (or to be more correct : "cracker") changed the code in some way only he knows. So all errors are thrown are very likely just messed up code wich isn't compatible with current MC 1.7.10 as it mainly was written for 1.6.4. THAT's the problem. So to solve it : go buy MC, login in to the official launcher with you account and you ready to go ...
btw : users using cracked clients are really unwanted in the MC-community and therefor most likely get bannend on the forums (as I know from Forge-forums). I would aggree if the FTB-team also enforces this "0 tolerance" policy.