php syntax error, unexpected T_OBJECT_OPERATOR-Collection of common programming errors

what I did is, I used a static field in my Database class, to store mysqli object. here is the code :

public static $Driver;

public static function Connect()
{
  self::$Driver = new mysqli(self::$Server, self::$DBUsername, self::$DBPassword, self::$DBName);
}

later, in another class, I want to use this static field. I tried this :

if (Database::Driver->errno != 0) return(false); else return(true);

and got this error for that line :

syntax error, unexpected T_OBJECT_OPERATOR …

can you tell me what I’m doing wrong?