You have a pin conflict .
See if you can change the conflicting pins. http://learn.adafruit.com/adafruit-wave-shield-audio-shield-for-arduino/faq
Pins 13, 12, 11 are always used by the SD card (they are the only pins that have a high speed SPI interface). Then there are 5 other pins used to talk to the DAC and SD card, but they can be set to connect to any arduino pin. However, by default, the library is configured to use pins 10 (for SD card) and pins 2, 3, 4 and 5 for the DAC. To chanage these pins requires modifying the library - the pins are referenced by their 'hardware' pin names (ie PORTD, etc) not by arduino pins.http://arduino.cc/en/Main/ArduinoEthernetShield
Arduino communicates with both the W5100 and SD card using the SPI bus (through the ICSP header). This is on digital pins 10, 11, 12, and 13 on the Uno and pins 50, 51, and 52 on the Mega. On both boards, pin 10 is used to select the W5100 and pin 4 for the SD card.