I received a gift of a Adafruit Wave shield and after assembling it using the excellent instructions on the Adafruit site I could not get it too work. The problem was the SD card would not initialize. After trying two different SD cards, checking the forums, and re-checking all my solder joints I could not get it too work. I decided to test the SD cards with an ethernet shield I also have for the Arduino. The SD cards refused to work in this shield as well. After a bit more reading I discovered that the issue was the SPI ports on my Arduino Mega are in different locations. The following fix also works for the Mega 1280.
The SPI pins on the Mega are 50, 51, and 52. The card select pin also needs to be changed from pin 10 to pin 53. The same modification also works for the SD card on the Ethernet Shield.
10 –> 53
11 –> 50
12 –> 51
13 –> 52