Hi PaulS
I just did some try outs here and I meraculously succeeded in getting the program to work.
Here's the story:
I decided to try out the program back at Arduino Playground - ParallaxRFIDreadwritemodule that reads the newer EM4x50 tags.
Again nothing happens when I scan the cards for obvious reasons.
So I used the first program again and somehow the whole thing works properly.
Probably the input wires were a little loose or there is a small mistake in the code when I tried to use it earlier. But everythings fine now.
Sorry for all the trouble I caused and thanks for trying to help me out.