ARDUINO MEGA 2560 SPI PROBLEM

Hi all,

I have got an arduino mega 2560 with an arduino usb host shield on top of it. I am trying to connect to another SPI device by wiring pins 50, 51, 52, 53 to the device, but its not working.

I understand that the host shield works via the ICSP header and uses pin 10 as its chip select. Without the host shield, my other device works perfectly and I can communicate to it. However, with the host shield on top of it, even though I am not pulling its chip select low, it doesn't seem to work with my other SPI device.

Any ideas why the host shield is blocking it?

Thanks in advance