Arduino mega + Adafruit NFC Shield PN532- Parts of message being changed.

I have a arduino mega with the adafruit nfc shield which I send messages to from an android phone using NFC.
However after a certain size of message, parts of the message are altered in transit.
I am expecting:
But I receive:

It always seems like the message is the same up to the 56th byte, but changes after that and is different every time I send one.
Anyone have any ideas what could be causing this?

If the message is small it arrives no problem without any changes, however I need to be able to send larger messages. So far from what i have tried i can send messages of up to 54 bytes, anything larger than that the message arrives different that sent by the phone.
Let me know if I should post any code.
Thanks for any help.

Solved the issue.
Incase anyone else runs in to the same problem have a look at the Adafruit_pn532 library. There is an array in there which you need to change the size of.

Thanks for taking the time to post an update jurasko! I'm sure anyone who has the same issue and finds this thread will be very grateful.