12 keys keypad, library error when uploading!!

zarobhr:
you might want to do as suggested and use a multimeter to map out the pins (shows how in the tutorial)
i mapped mine out and this was the combination i got although the keypad is. Not all keypads that seem to be the same wiring are the same wiring

123
456
789
C0E

const byte rows = 4; //four rows

const byte cols = 3; //three columns
char keys[rows][cols] = {
  {'1','4','7'},
  {'2','5','8'},
  {'3','6','9'},
  {'C','0','E'}
};

Yhap, but the mapping it's not the problem...
It seems that when I pressed keys 2, 4, 6, 8 and 0 the Arduino just doesn't recognized them.

I'm not sure how the keypad works internally but I think it's based on the Voltage Divider Principle, with voltage drops between the keys that can tell wich of the key is being pressed.
Is it possible that the resistors drop less voltage than the library it's configured for?