if you bought it on ebay, often the libs are not uptodate.
Use the New LiquidCrystal lib by fm. It works. I have one lcd as your.
the sketch preamble working with me is as follows
#include <Wire.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE); // Addr, En, Rw, Rs, d4, d5, d6, d7, backlighpin, polarity
The lib replace the standard one but has several advantages.
Delete the old and rename the directory LiquidCrystal_I2C.
LCD.h is inside