My phone won't get internet, what should I do?

I have a mytouch 3g and it receives the signal from the wifi at my house but when I try to access internet content it says there is a "network error". I'm pretty sure its not the phone because it connects to wifi elsewhere but just not on this router at my house. It seams to work just fine when I don't encrypt the signal but the other people in the house want it that way. Can anyone help???