In a new scene: Try enabling 'use limits' with IK turned off(before loading .bvh), if that still isnt enough, try changing limits to lower values on offending body parts(usually r&l shoulder, collars and/or neck). As Cage points out, there are many files that aren't compatible with posers naming conventions. I've seen files where the collars are named shoulder and shoulders are called upper arms for example. BVHacker(IMHO) should be in every animators toolbox, not only can you rename body parts but you can also reset start(or)stop coordinates to zero(or any other coordinate) ,rotation(only on first frame at root/body level) or trim animation if desired.

Y'all have a great day.