NFC PN532 Interfacing with a mobile App

Hello guys !

I'm working on an Arduino/ Mobile App interfacing using NFC protocol (PN532 Sheild ).

I'm following this tutorial to initiate :

while testing this the code below I had an error telling me

Found an ISO14443A card/tag
  UID Length: 4 bytes
  UID Value: 0xE0 0xB7 0x51 0x55
Seems to be a Mifare Classic card (4 byte UID)
Reformatting card for Mifare Classic (please don't touch it!) ... 
Authentication failed for sector 16
Place your NDEF formatted Mifare Classic 1K card on the reader
and press any key to continue ...

please help !