Linksys Wireless Router :: Toshiba Laptop With Atheros AR5008X Won't Connect

I have three N-compliant devices and several G-compliant devices on my network. I also have two routers, one being used an an access point. The first is a Linksys WRT350N; the second is a Linksys WRT54G. I have the G router connected as an access point so that I can reserve the N router for the N devices and achieve N speeds.N devices:Toshiba laptop; network adapter is Intel 4965AGN.Toshiba laptop; network adapter is Atheros AR5008XLexmark Wireless printerRouter settings:WRT350N: Security Mode WPA2 Personal; Encryption AES; Network Mode N-only; Radio Band 40MHz.WRT54G: Security Mode WPA Personal; Encryption AES; Network Mode MixedThe best I can recall, I set the WRT54G to WPA Personal instead of WPA2 Personal because one of the G-compliant devices did not list the WPA2 Personal setting -- but this is based on memory only.To reserve the WRT350N for the N devices and achieve N speeds, I set the Wireless Mode to N-only and Radio Band to 40MHz., and each router broadcasts its own unique SSID. Once I set everything up, I saw a substantial increase in the link speed reported by the Toshiba Connectivity Doctor (I realize there are issues about taking these numbers at face value, but let me continue). The Toshiba Connectivity Doctor reported WRT350N link speed at 130 Mbps and everything appeared to be working well.PROBLEMUntil recently, no problems were apparent; the Toshiba Connectivity Doctor indicated the two laptops connected to the WRT350N at 130 Mbps, the printer connected to and printed via the WRT350N, and all G devices connected through the WRT54G. Recently, however, network performance declined and the Toshiba Connectivity Doctor indicated erratic link speeds ranging from 1 Mbps to 130 Mbps.I found through a little research that my quest to reserve the WRT350N router for N devices lacked one element: according to Linksys info for the router, setting the N Transmission Rate to anything other than Auto results in denying access to B/G clients.I set the N Transmission Rate to 270 Mbps (the highest setting). The Linksys printer works fine and the Toshiba Connectivity Doctor indicates a solid 130 Mbps link speed for the Toshiba laptop with the Intel 4965AGN adapter card.The other Toshiba (with the Atheros AR5008X adapter card), however, is now only able to connect to the WRT54G (the Toshiba Connectivity Doctor indicates a solid link speed of 54 Mbps to the G SSID). If I reset the WRT350N N Transmission Rate to Auto, the Toshiba with the Atheros card can once again connect to the N Router -- but the erratic link speeds and the network degradation returns also.I have verified that the Atheros AR5008X network adapter is N-compliant. There aren't many settings on the Atheros AR5008X adapter card configuration, but I can find no documentation on the Internet for this card.As far as I can determine, all firmware is up to date for both routers and all drivers are up to date for both adapter cards.I'd love to know what changed in the first place, but I'm more concerned with fixing this problem. How I can get the Atheros adapter card to connect to the WRT350N with the N Transmission Rate set to something other than Auto?