NXT Motor, rotary encoders and Arduino

Hello,
A brife intro, i study interaction design at Kolding school of Design, and is working on a project involving elderly on nursing homes.
So I have an Nxt Motor → Motor sheild → Arduino and i want to controle an piston going up and down like this

Why the NXT motor and not an servo/stepper you might ask, I want to hook to pistons up so when number 1. is pressed the piston on nr. 2. will rise, like this - and we can not do this with steppers ore servos.

i got most of i hooked up as you can see the motor is on M2 of the motor shield and every thing is hooked up to the remaining pins

The pushbutton is used to control forward/backward and is on digital pin(2)
The potentiometer is used to control speed of the motor and is on analog pin(2)
and all of that is working fine, i can manually control the direction and the speed, but i would like to get those informations from the rotary encoder so i can control the position of the motor and piston. I know the the rotary encoder communicates owed i2c witch is on analog pin 4 and 5 but i have tried every sketch that i can find that has something to do with rotary encoders but can’t seem to get them to work properly if i try using the I2C_Scanner ore NXTMMX_ReadEncoders examples that comes with the NXTI2CDevice library i doesn’t find the motor - but when i turn the wheel on the motor the serial monitor will display that the sketch is running but noting els than the text in the program is displayed in serial monitor e.g…
when running the I2C_Scanner sketch:
starting the sketch and starting serial monitor while display:

Scanning 2 to 40 ...
Checking Address 2 ....

and when i start turning the motor the text starts displaying, and when i stop turning the motor the text stop appearing, so it seems like there is some sort of communication/transmission going on but i can’t seem to get i to work.

Checking Address 4 .... no device found.
Checking Address 6 .... no device found.
Checking Address 8 .... no device found.
Checking Address 10 .... no device found.
Checking Address 12 .... no device found.
Checking Address 14 .... no device found.
Checking Address 16 .... no device found.
Checking Address 18 .... no device found.
Checking Address 20 .... no device found.
Checking Address 22 .... no device found.
Checking Address 24 .... no device found.
Checking Address 26 .... no device found.
Checking Address 28 .... no device found.
Checking Address 30 .... no device found.
Checking Address 32 .... no device found.
Checking Address 34 .... no device found.
Checking Address 36 .... no device found.
Checking Address 38 .... no device found.
Checking Address 40 .... no device found.
I2C Scan Complete.

I hope any body can help me, and by the way I don’t have time to get and nxt motor shield because there are no retailers in denmark

//PeterOK