Linksys Wireless Router :: WRT120n - Intermittent Connection For Apple Devices

I recently upgraded my Linksys wrt120n router firmware & had to reconfigure settings.  Subsequently, some (but not all) of my apple devices are having intermittent wireless connection problems.  Specifically, my ipad1 & ipad2 never lose their connection but a mac book pro (~ 2 years old), iPhone 3g, iPhone 4, older iPod touch & very old i book g4 all work for a period of time (usually 1/2 day) & then lose their connection.  When I attempt to reconnect these devices I receive the following error..."unable to join the network xxxxxx....".  I also have a Dell laptop (1 1/2 yrs old) that generally does not have the connection problem.  Finally, when the devices do lose their network connection all I have to do to reconnect is go to the Linkys router setup webpage & click on save & the wireless connection works again (almost like this is just refreshing the connection for these specific apple devices).  I was not having any problem prior to the firmware upgrade & from what I have read the older firmware version is no longer available so going back to the old firmware does not appear to be an option.