Linksys E1200-Connecting (2)Iphone 4 and Ipad to WAP

I just bought a Linksys E1200 wireless router, last night. I tried logging on to the WAP side, and could not get it to work on any of my 3 devices. I saw the full signal on the Wi-Fi...but when I tried to connect it would just cycle, and then give me a pop-up that read,"Unable to connect to (said) network.". I can change the router to WEP, and everything works fine. But the point of getting the newer WAP protection, is for better security. Any thoughts on how to make my 3 devices work on the WAP? Thanks for any help.