Unable to remove a directory from crowd: could not execute statement

2016-02-02 16:20:58,927 http-bio-18095-exec-4 WARN [engine.jdbc.spi.SqlExceptionHelper] SQL Error: 0, SQLState: 23503
2016-02-02 16:20:58,927 http-bio-18095-exec-4 ERROR [engine.jdbc.spi.SqlExceptionHelper] ERROR: update or delete on table "cwd_user" violates foreign key constraint "fk_user_attribute_id_user_id" on table "cwd_user_attribute"
  Detail: Key (id)=(16220293) is still referenced from table "cwd_user_attribute".
2016-02-02 16:20:58,928 http-bio-18095-exec-4 ERROR [console.action.directory.RemoveDirectory] could not execute statement
org.hibernate.exception.ConstraintViolationException: could not execute statement
	at org.hibernate.exception.internal.SQLStateConversionDelegate.convert(SQLStateConversionDelegate.java:129)
	at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49)
	at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:124)
	at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:109)
	at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:189)
	at org.hibernate.hql.internal.ast.exec.BasicExecutor.doExecute(BasicExecutor.java:108)