Serial outputting an error string of x and o characters

I'm currently trying to implement an edited version of the CharlieBearV2.pde sketch from the Charlie's RFID Bear project on Makezine. Beforehand, I tested the RFID reader (I'm using an ID12 from Sparkfun) to make sure all my RFID tags register, which they do, and I used the default Adafruit Wave Shield library to test the playing of sound on the Arduino, which it does. Unfortunately, my edited version of the CharlieBearV2.pde program does not read the RFID tags, play music, or even outputs the programmed error messages in the serial monitor. Instead, it's printing out a string of x and o characters that I cannot copy correctly. When I try to paste it, it only appears as "xxx." The error only appears when I plug in my Wave Shield.

Here's the output on my serial monitor:

I'm really not sure what to make of this; Google has been unhelpful. As for the CharlieBearV2.pde program, I made minor changes to suit my RFID tags and MP3 files; the edits are thus:

#define ENABLE 7      // Set the pin number for enabling the RFID reader. The Audio Shield uses pins 2-5.
#define NUMTAGS 5

int  val = 0; 
char code[10];
int bytesread = 0; 

char knowntags[NUMTAGS][11] = {"6A004A0A55", "6A004A0DE6", "6A004A0EB7", "6A0049EBEE", "6A0049E500"};
char soundfiles[NUMTAGS][15] = {"6A004A0A55.WAV", "6A004A0DE6.WAV", "6A004A0EB7.WAV", "6A0049EBEE.WAV"};
char filename[1][15];

Thank you for reading this!

  Serial.begin([glow=red,2,300] 2400 [/glow]);  // RFID reader SOUT pin connected to Serial RX pin at 2400bps

I suspect you are using the wrong baud rate in the serial monitor, but it's a bit hard to tell in the absence of all your code.