Question : foreign key constraint error question

I have the following tables

CREATE TABLE `w_document_flat` (
  `Accession_No` varchar(7) NOT NULL,
  `Pub_Abbreviation` varchar(25) NOT NULL,
  PRIMARY KEY  (`Accession_No`)
) ENGINE=MyISAM

CREATE TABLE `descriptors` (
  `descriptor_id` int(11) NOT NULL auto_increment,
  `descriptor_name` varchar(500) NOT NULL,
  PRIMARY KEY  (`descriptor_id`)
) ENGINE=InnoDB

CREATE TABLE `w_descriptors` (
  `descriptor_id` int(11) NOT NULL,
  `Accession_No` varchar(7) NOT NULL,
  PRIMARY KEY  (`descriptor_id`,`Accession_No`),
  KEY `Accession_No` (`Accession_No`),
  KEY `descriptor_id` (`descriptor_id`),
  CONSTRAINT `Accession_No` FOREIGN KEY (`Accession_No`) REFERENCES `w_document_flat` (`Accession_No`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  CONSTRAINT `descriptor_id` FOREIGN KEY (`descriptor_id`) REFERENCES `descriptors` (`descriptor_id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB

When I try and do an insert into the
insert into w_descriptors (descriptor_id, Accession_No) values ("0000001", 1);

I get the following message:
Error Code: 1452
Cannot add or update a child row: a foreign key constraint fails (`w/w_descriptors`, CONSTRAINT `Accession_No` FOREIGN KEY (`Accession_No`) REFERENCES `w_document_flat` (`Accession_No`) ON DELETE NO ACTION ON UPDATE NO ACTION)

I am really confused.  Is it because the w_document_flat table is MyISAM?  

Answer : foreign key constraint error question

Yes, "Both tables must be InnoDB tables and they must not be TEMPORARY tables. "

http://dev.mysql.com/doc/refman/5.1/en/innodb-foreign-key-constraints.html

I ran into the same problem recently.