Mega WiFi Problems

I am testing various WiFi shields with Arduino Mega, but I am facing problems to connect.
I have used Adafruit's CC3000 shield, but it does not connect. The shield with the code works perfectly on an Uno, but not on Mega. I have adjusted the pins to work on the Mega (measured them as well), and everything concerning hardware/software seems to be configured fine. However, it does not work.

Does any of you know why this is happening? Maybe a problem with the Mega?

Because I have also tried to use the ElecFreaks CC3000 shield as well, and the WiFly but none of them works!!!!!!!!!