MySQL Cannot Add Foreign Key Constraint

So I'm trying to add Foreign Key constraints to my database as a project requirement and it worked the first time or two on different tables, but I have two tables on which I get an error when trying to add the Foreign Key Constraints. The error message that I get is: > ERROR 1215 (HY000): Cannot add foreign key constraint This is the SQL I'm using to create the tables, the two offending tables are `Patient` and `Appointment`. SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0; SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=1; SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='TRADITIONAL,ALLOW_INVALID_DATES'; CREATE SCHEMA IF NOT EXISTS `doctorsoffice` DEFAULT CHARACTER SET utf8 ; USE `doctorsoffice` ; -- ----------------------------------------------------- -- Table `doctorsoffice`.`doctor` -- ----------------------------------------------------- DROP TABLE IF EXISTS `doctorsoffice`.`doctor` ; CREATE TABLE IF NOT EXISTS `doctorsoffice`.`doctor` ( `DoctorID` INT(11) NOT NULL AUTO_INCREMENT , `FName` VARCHAR(20) NULL DEFAULT NULL , `LName` VARCHAR(20) NULL DEFAULT NULL , `Gender` VARCHAR(1) NULL DEFAULT NULL , `Specialty` VARCHAR(40) NOT NULL DEFAULT 'General Practitioner' , UNIQUE INDEX `DoctorID` (`DoctorID` ASC) , PRIMARY KEY (`DoctorID`) ) ENGINE = InnoDB DEFAULT CHARACTER SET = utf8; -- ----------------------------------------------------- -- Table `doctorsoffice`.`medicalhistory` -- ----------------------------------------------------- DROP TABLE IF EXISTS `doctorsoffice`.`medicalhistory` ; CREATE TABLE IF NOT EXISTS `doctorsoffice`.`medicalhistory` ( `MedicalHistoryID` INT(11) NOT NULL AUTO_INCREMENT , `Allergies` TEXT NULL DEFAULT NULL , `Medications` TEXT NULL DEFAULT NULL , `ExistingConditions` TEXT NULL DEFAULT NULL , `Misc` TEXT NULL DEFAULT NULL , UNIQUE INDEX `MedicalHistoryID` (`MedicalHistoryID` ASC) , PRIMARY KEY (`MedicalHistoryID`) ) ENGINE = InnoDB DEFAULT CHARACTER SET = utf8; -- ----------------------------------------------------- -- Table `doctorsoffice`.`Patient` -- ----------------------------------------------------- DROP TABLE IF EXISTS `doctorsoffice`.`Patient` ; CREATE TABLE IF NOT EXISTS `doctorsoffice`.`Patient` ( `PatientID` INT unsigned NOT NULL AUTO_INCREMENT , `FName` VARCHAR(30) NULL , `LName` VARCHAR(45) NULL , `Gender` CHAR NULL , `DOB` DATE NULL , `SSN` DOUBLE NULL , `MedicalHistory` smallint(5) unsigned NOT NULL, `PrimaryPhysician` smallint(5) unsigned NOT NULL, PRIMARY KEY (`PatientID`) , UNIQUE INDEX `PatientID_UNIQUE` (`PatientID` ASC) , CONSTRAINT `FK_MedicalHistory` FOREIGN KEY (`MEdicalHistor...