Ohh i figured out what was wrong... Sparkfun has configured the SerLCD wrongly, the manual says it should be coded to the right LCD when you buy it "pre fixed". But apparently it's set to 2x16 instead 4x20, now i just need to figure out how to reprogram the Serial LCD module.
edit:
Hmm the data sheet says i need to: "transmit the special command - 124 (0x7C) Follow this command with either 3, 4, 5 or 6.
So i would think i had to send the command
Serial.print(0x7C, BYTE);
Serial.print(3, BYTE); (3 for a 20 Chacter wide display)
and
*Serial.print(5, BYTE); * (4 for a 4 line display)
But it doesn't work, i guess i shouldn't send the "Serial.print" command but something else insted?
Datasheet:
edit2: Damn im stupid
it of course needed to be:
Serial.print(0x7C, BYTE);
Serial.print(0x03, BYTE);
well problem solved 