FOR statement variable "<str>" is read only

  Explanation:  (a) If the variable is on a FOR cursor loop then
  this variable and the select list value names are considered
  constant (i.e.  read only) within the FOR body.  (b) If the
  variable is on a FOR counted loop then this variable needs to be
  updated by the FOR loop but can not be changed because it is
  declared as CONSTANT.

  User Action:  (a) Use the UPDATE ...  WHERE CURRENT OF statement
  to update rows fetched by the FOR cursor loop.  (b) Change the
  variable declaration to be UPDATABLE or use another variable
  name for the loop