MySQL Forums :: Foreign Keys (Referential Integrity) :: error in inserting to foreign key column from mastert table

i have createdd two tables having foreign key relationship the tables are
CREATE TABLE fee_class_category (
class_category_id INTEGER UNSIGNED NOT NULL AUTO_INCREMENT,
class_from SMALLINT UNSIGNED NULL,
class_to SMALLINT UNSIGNED NULL,
PRIMARY KEY(class_category_id)
)
TYPE=InnoDB;
CREATE TABLE fee_class_category_name (
class_category_name VARCHAR(15) NOT NULL,
class_category_id INTEGER UNSIGNED NOT NULL,
class_category_name_id SMALLINT UNSIGNED NULL,
PRIMARY KEY(class_category_name),
FOREIGN KEY(class_category_id)
REFERENCES fee_class_category(class_category_id)
ON DELETE NO ACTION
ON UPDATE NO ACTION
)
TYPE=InnoDB;

when i am trying to insert values from class_category_id column from fee_class_category into class_category_id column of fee_class_category_name table. it is showing below error
Error Code : 1062
Duplicate entry '' for key 1