Error 1022 – Can’t write; duplicate key in table

I’m getting a 1022 error regarding duplicate keys on create table command. Having looked at the query, I can’t understand where the duplication is taking place. Can anyone else see it?

SQL query:

-- -----------------------------------------------------
-- Table `apptwo`.`usercircle`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS  `apptwo`.`usercircle` (

 `idUserCircle` MEDIUMINT NOT NULL ,
 `userId` MEDIUMINT NULL ,
 `circleId` MEDIUMINT NULL ,
 `authUser` BINARY NULL ,
 `authOwner` BINARY NULL ,
 `startDate` DATETIME NULL ,
 `endDate` DATETIME NULL ,
PRIMARY KEY (  `idUserCircle` ) ,
INDEX  `iduser_idx` (  `userId` ASC ) ,
INDEX  `idcategory_idx` (  `circleId` ASC ) ,
CONSTRAINT  `iduser` FOREIGN KEY (  `userId` ) REFERENCES  `apptwo`.`user` (
`idUser`
) ON DELETE NO ACTION ON UPDATE NO ACTION ,
CONSTRAINT  `idcategory` FOREIGN KEY (  `circleId` ) REFERENCES  `apptwo`.`circle` (
`idCircle`
) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE = INNODB;

MySQL said: Documentation

#1022 - Can't write; duplicate key in table 'usercircle'