(click image for larger view)

amy_aimei,

I have had a quick look at the BeachVolleyballTop, and the specific problem on the shoulder straps that happens in the LegUp pose with the hands behind the head. It seemed to me to be a joint parameter problem, so I played around until I found a fix. The problem with changing a JP, is that in fixing one problem, it is easy to create others. After a quick check I can't see any new problems, but I do not have time for really thorough testing of the fix.

[edit]
In the Joint Editor I changed the 'Static A' parameter in the 'Swing' channel of the Left Shoulder to a value of 139.735 (see image above) ,  then used Symmetry Left to Right to copy the PJs to the other shoulder.