Issues with PN532 shield and Keybord.h library. Need help!

[johnwasser]

Looks like you forgot to call Keyboard.begin();

EDIT: Oops... My mistake. You call it FOR EACH CARD READ.

@Davessi

    Keyboard.begin(); 
     if (cardid == 1839898475)
      Keyboard.press("A");
       delay(100);
      Keyboard.release("A");
       delay(2000);
    Keyboard.end(); 

WARNING: C++ is not like Python. It doesn't care about indentation. Your code means:

    Keyboard.begin(); 
    if (cardid == 1839898475)
    {
      Keyboard.press("A");
    }
    delay(100);
    Keyboard.release("A");
    delay(2000);
    Keyboard.end(); 

That's going to call Keyboard.begin();, Keyboard.release("A"); and Keyboard.end(); for each card read, regardless of ID.