Hey guys, really sorry to bump up such an old thread but I search & found this which is basically the same problem I'm having.
Im using a linksys WRT150N router, tried everything mentioned in this thread except flashing the router - because I'm already on the latest firmware v1.01.9.

The only other option i seem to have is flashing the router with DD-WRT firmware which is a custom 3rd party bit of software.
http://www.dd-wrt.com/wiki/index.php/Main_Page

I just think its quite a drastic thing to do & I have no guarantee it will fix my issues, it was an official firmware upgrade that the guy above me did to fix his prob.
ANy advice to consider before I take the plunge & void my routers warranty? I only got my N800 yesterday & it worked fine with my router last night, as did the OP's when he had the problem. it just wont reconnect now!
Halp!