relation <str> is part of join cannot be updated

  Explanation:  You tried  to  modify  or  erase  records  from  a
  relation  that  is  joined  (using  the CROSS clause) with other
  relations.

  User Action:  Redefine the query so that the  relation  you  are
  trying  to  update  is  not  directly joined to other relations.
  i.e.  do not use a CROSS clause, but instead represent the other
  relation references as subqueries.