The dreaded word you don't want to hear with shoulder pain is impingement.  When citing impingement,  I am talking about supraspinatus impingment, (one of the four rotator cuffs) where the tendon becomes caught (or impinged) under the 'acromion process'.  This usually results in pain in the anterior (front) aspect of the shoulder and any movement involving raising of the arm, either directly in front of you or to the side, results in acute pain and an inability to hold the arm for any length of time.