Clliper not releasing

Crack open the bleeder screw and see if some fluid shoots out and it loosens up or not! If it does, I would look at replacing the brake hoses(Both sides!) They may look ok on the outside, but be bad on the inside. Know why brake fluid turns black over time? It's from the deteriorating hoses. In time they can internally collapse and block the fluid from releasing. You also need to lube where the caliper is sliding at with good High temp Caliper grease. Or you just did something else wrong. Was the same side not releasing before you took the brakes apart?