Hello Ashley,
If the serial number read is totall wrong, it is most likely the serial number of another card. The issue can be related to the fact that two cards entered the printer, and maybe both are in the field of the reader. To avoid that two cards are in the printer simultaneously, it is important to set sufficiently big time delays in the printer options window, contactless tab. On some printer models it can happen that a card falls into the bottom section of the printer, invisible to us, but not to the MIFARE reader.
regards,
Rutger.
Rutger Koperdraad
Senior Software Engineer
"A reasonable man adapts himself to the world. The unreasonable man persists in trying to adapt the world to himself. All progress, therefore, depends on the unreasonable man." (Bernard Shaw)