to the forum.
I know it's little use in your circumstances, but I have a similar problem with my laptop (Dell) which appears to maintain its wireless connection to my Belkin router even when its gone to sleep and been re-awakened, but won't connect to anything (even the router config screen). I find in my case that stopping, ejecting and re-inserting the wireless card is the quickest way to restore things.
I had thought this was just down to naff programming on Belkin's part (the wifi card and driver software is also belkin) so I'm sorry to hear Linksys are at it too, especially if they have introduced this problem as a result of a firmware update.
I suppose the update may have introduced a compatibility issue with your laptop's wireless card or its driver - have you checked for updates for that? Failing that, there are a number of Linksys users on this forum, hopefully one of them will have an idea.