Problem using Groove's Serial LCD with Attiny85

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Hi everyone!

I'm working in a communication between boards project, and wanted to use an LCD screen I got from SeedStudio, specifically this: http://www.seeedstudio.com/wiki/Grove_-_Serial_LCD (version 1.1)

For that purpose, I tried to use the library provided in the link above (SerialLCD). Uploaded the HelloWorld example [code at the bottom] to the Attiny (having previously changed pins 11 and 12 to 0 and 1), using the Arduino as ISP, with no problem. But, unfortunately, didn't work (nothing displayed, both red and green LEDs on). After checking connections, re-uploading, and resetting everyting with no success, I decided to look for other options.

I found another library, LiquidCrystal_I2C (following this tutorial), but happened exactly the same as before (no text nor backlight, and both leds on).

I've also read about some modifications of LiquidCrystal_I2C library, and tried a couple of them, with the same result.

LCD and Attiny both work properly.

[HelloWorld example]

/*
  SerialLCD Library - Hello World
 
 Demonstrates the use a 16x2 LCD SerialLCD driver from Seeedstudio.
 
 This sketch prints "Hello, Seeeduino!" to the LCD
 and shows the time.
 
 Library originally added 16 Dec. 2010
 by Jimbo.we 
 http://www.seeedstudio.com
 */

// include the library code:
#include <SerialLCD.h>
#include <SoftwareSerial.h> //this is a must

// initialize the library
SerialLCD slcd(11,12);//this is a must, assign soft serial pins

void setup() {
  // set up
  slcd.begin();
  // Print a message to the LCD.
  slcd.print("hello, world!");
}

void loop() {
  // set the cursor to column 0, line 1
  // (note: line 1 is the second row, since counting begins with 0):
  slcd.setCursor(0, 1);
  // print the number of seconds since reset:
  slcd.print(millis()/1000,DEC);
}

Any ideas?

Thanks!