Animation

Doing my head in!!!!! The keyframing is fine and all understandable but for some reason when I move the bone or amature it wont move to that position but do a half movement or less, only choosing to move in someways and not in others. Very frustrating, have been trying to fix and playing round with for ages.....not sure if I've stuffed something up earlier in the rigging, and if I did am finding it very difficult to figure out what it is!