unique Relation constraint <str> does not exist in this database

  Explanation:  The relation-specific constraint specified  either
  was  not found in the database or does not reference a UNIQUE or
  PRIMARY KEY constraint.  This  relation-specific  constraint  is
  referenced  by  the  definition  of  a  FOREIGN  KEY  REFERENCES
  relation-specific constraint and must represent either a  UNIQUE
  or  PRIMARY  KEY  for the referenced relation and any referenced
  fields.

  User Action:  Contact your  Oracle  support  representative  for
  assistance.