Front wheel and or front rotors could be backwards if the rotors were removed separately. Front wheel has a directional arrow and s do the rotors.This could be caused by several things. First, the caliper pistons could be stuck in the braking position due to a buildup of gunk on them or the pad slide pins. Second, you could have got the axle spacers in the wrong locations which would shift the wheel right or left and bind up the rotor against a brake bad. Which brake is it, front or back? What kind of bike, 1300 or 1800?