I just upgraded to the Jetpack 4G MiFi 5510L. My Dell laptops connected immediately, but our Apple laptop does not connect. it sees the signal, just will not connect.
Your password is most likely incorrectly entered on your Apple laptop.
Try viewing your wireless profiles on the laptop and deleting them. When the profiles are gone then try to connect again. The Apple laptop should be smart enough to detect the security parameters of the MiFi 5510L so that all you need to do is enter the correct WiFi password.