errno:150“外键约束格式不正确”）

DROP DATABASE IF EXISTS AgenceAssurance;
CREATE DATABASE IF NOT EXISTS AgenceAssurance;
USE AgenceAssurance;

CREATE TABLE Logininfo (
  idLogin    INT(3)  PRIMARY KEY  NOT NULL AUTO_INCREMENT,
  userName       VARCHAR(50) NOT NULL,
  pass       VARCHAR(50),
  usertype   VARCHAR(50)          DEFAULT NULL,
  GrantedKey VARCHAR(8)           DEFAULT NULL
)ENGINE = InnoDB;

CREATE TABLE Operation (
  idOpt    INT PRIMARY KEY  NOT NULL AUTO_INCREMENT,
  libelOpt TEXT,
  dateOpt  DATETIME DEFAULT now(),
  userName VARCHAR(50),
   CONSTRAINT fk_login FOREIGN KEY (userName) REFERENCES Logininfo (userName)
)ENGINE = InnoDB;

错误SQL查询：

CREATE TABLE Operation (
  idOpt    INT PRIMARY KEY  NOT NULL AUTO_INCREMENT,
  libelOpt TEXT,
  dateOpt  DATETIME DEFAULT now(),
  userName VARCHAR(50),
  CONSTRAINT fk_login FOREIGN KEY (userName) REFERENCES Logininfo (userName)
)ENGINE = InnoDB

mysql说：

1005-无法创建表agencasurance.operation（errno:150“外键约束格式不正确”）（详细信息…）