PSP Go will not connect to Playstation Store through Apple Airport Extreme

I bought my PSP Go in October and I use an Apple Extreme Base Station. Initially everything worked fine and my problem started just recently when I tried to sign in to the Playstation Store again after being inactive for a while. We have 2 PSPs in our household and these problems are the same for both of them.

I am experiencing a lot of difficulty in connecting to the Playstation Store with my PSPs. I usually get some kind of error message and usually a different error message/code each time. When trying to log on to the Playstation Store, I quite often make it as far as the "sign in" screen, but it seems to stop there. It either times out, gets a DNS error or if I get as far as the DNAS screen, I'll get some kind of error message related to that. Once in a blue moon will I actually get signed in to the Playstation store. When I test PSPs wireless internet connection, it will connect to the internet quite frequently, but hardly ever succeed when I try to sign in to the Playstation Store.

I took my PSP Go to work with me, for troubleshooting and not playing, and I managed to sign in straight away and repeated it several times. When I got home that same afternoon, I couldn't get on. We dont use Apple Airport Extreme at work. We also have a different ISP.

I called my ISP to see if they knew what was going on. I was told that Sony uses UPnP to communicate whereas Apple uses NAT-PMP and that might cause trouble. Also I might have to enable NAT in my router. There is nothing they can do. I checked and NAT is enabled and always has been as far as I know.

Since I didn't get anywhere with my ISP, I thought I'd try calling AppleCare Protection Plan but they were unable to offer any assistance whatsoever, other than that they had never heard of such a problem before. There were no similar problems reported in their database and that concluded the support they had to offer.

Although I have no IT or Network competence at all, I'm confident it is some kind of communication problem between my PSP Go and the Apple Airport Extreme Base station. I can tell that the PSP gains access to the network, the times it is successful in obtaining an IP address, and that it automatically gets on to the 802.11b as it should. I can see the client along with its MAC address on the routers statistics window showing wireless clients. I still get a connection error, 80435062 was the one that came up last. Other times a DNAS error occurs and the operation times out. I have been through a lot of different error codes. There doesn't seem to be any logic to the errors being reported. Operation times out comes up most often, though. These codes are PSP error messages.

The PSP Go is set up with the same encryption as the router (WPA-PSK (TKIP)) and it has the correct key/password. It is obviously correct as it works from time to time. I've even tried turning the security off without that making any difference whatsoever. At work there is a 26 digit WEP key to gain access.

I have a PC and an iMac and I can log on to the PSN with both of them. I have a PS3 that I can log onto the Playstation Network and Playstation Store with. All these things go through the same Apple Extreme Base Station. The iMac is the only thing, other than the PSPs that has a wireless connection. The others (PS3 & PC) use an ethernet cable.

Does anybody in this forum have any idea what my problem could be? Could it be something to do with the Playstation Store IP address for PSPs? Or is it a fundamental SONY/Apple communication problem?

Any help will be immensely appreciated.