Hey guys, I think I've found a solution. I'm using a Linksys WRT160n v.3 with custom firmware (DDWRT), and I had the unable to join wifi network message multiple times. I even reset my network settings multiple times which didn't help.
Then I remembered reading this support page from Apple:
http://support.apple.com/kb/TS3304
So, I set my router to G only and renamed that to whatever
G then I tried to connected to it, and it worked! I'm now connected to my router so give it a try guys. I hope this helps
EDIT: Apparently, when I set it to B,G,N (mixed and my default from when I first started off with the problems) then I get the unable to connect message again. But B and G mixed is perfectly fine. Go figure.