Could you explain a little further? I've just resorted my iPad and the same issue popped up. I've tried to reset the router and then re-enter my credentials but the same thing happened.
Yeah, it seems like youre losing your IP then not authenticating when the router attempts to reissue. Ive seen this behavior in the past, usually with mixed security (like WEP, WPA, WPA/2 devices all on the same router), and sometimes peculiar behavior with mixed protocols (like B/G/N).
Sometimes it just cant be helped because of the devices, especially less updatable things like TVs, DVRs, etc.
As a side note, make sure youve got the latest router firmware. Generally you download a file from the manufacturer, then upload it using the router web UI.
Id just work through each potential failure point: DHCP, security, maybe start with setting up a static IP on the device (I do this anyway, as I like to have specific IPs for specific machines/devices in my network). Then maybe try running without any security (obviously not for any extended time!)
Doh! Time to make the taco bar ... back a bit later