MySql外键约束和PHP

Question

So I'm having trouble creating two databases called role_perm and user_role. I just couldn't find out where the problem is, since it shows me:

Foreign key constraint is incorrectly formed

For both role_perm and user_role, there are five procedures that automatically creates my DBs, these codes are my MySQL codes...

CREATE TABLE `users` (
    ID INT(8) NOT NULL AUTO_INCREMENT,
    `username` VARCHAR(45) NOT NULL,
    `firstname` VARCHAR(45) NOT NULL,
    `lastname` VARCHAR(45) NOT NULL,
    `mobile` VARCHAR(45) NOT NULL,
    `home` VARCHAR(45) NOT NULL,
    PRIMARY KEY (`ID`)
) ENGINE = InnoDB;

CREATE TABLE `roles` (
    `role_id` INT(8) UNSIGNED NOT NULL AUTO_INCREMENT,
    `role_name` VARCHAR(50) NOT NULL,
    PRIMARY KEY (`role_id`)
) ENGINE = InnoDB;

CREATE TABLE `permissions` (
    `perm_id` INT(8) UNSIGNED NOT NULL AUTO_INCREMENT,
    `perm_desc` VARCHAR(50) NOT NULL,
    PRIMARY KEY (`perm_id`)
) ENGINE = InnoDB;

CREATE TABLE `role_perm` (
    `role_id` INT(8) UNSIGNED NOT NULL AUTO_INCREMENT,
    `perm_id` INT(8) NOT NULL,
    INDEX (`role_id`, `perm_id`),
    FOREIGN KEY (role_id) REFERENCES roles(role_id),
    FOREIGN KEY (perm_id) REFERENCES permissions(perm_id)
) ENGINE = InnoDB;

CREATE TABLE  `user_role` (
    `user_id` INT(8) UNSIGNED NOT NULL AUTO_INCREMENT,
    `role_id` INT(8) NOT NULL,
    INDEX (`user_id`, `role_id`),
    FOREIGN KEY (user_id) REFERENCES users.ID,
    FOREIGN KEY (role_id) REFERENCES roles.role_id
) ENGINE = InnoDB;