Seeing as how this was the top Google result for the exact problem I was experiencing and I spent 4+ hours researching the issue which led to its resolution, I registered to post this fix:
The issue, for me, was my adapter's driver. I had an old driver. My Atheros wireless adapter would not recognize WPA2 security. There were two options: Log in to my router and change my security to WEP (and slowing my speed in the process) or update my drivers. After searching for quite some time, I found my drivers here (of course, your adapter might be a different one): Quick tip: Atheros AR5007 wifi and Linksys routers - Roy Tanck's weblog
TL;DR: Update your drivers or use WEP security.
OP: Please mark your topic as SOLVED or RESOLVED or whatever this forum uses if this information was helpful.