context variable <str> is already defined

  Explanation:   The  current  statement  attempts  to  define  an
  existing  context variable such as the P in OPEN IN STREAM S FOR
  P IN PORT.  However,  the  context  variable  has  already  been
  defined in another RSE.

  User Action:  Use another context variable, or close the  stream
  in which the context variable is defined.