Wondering if anyone could shine some light on this?

Exhibit 1: 360 does not share media using WPA. Either on the dashboard or via Media Centre. It will connect but then a day later it will lose it's connection and will only come back after several attempts, but then go again. Live/online play works fine.

Exhibit 2: Laptop cannot see shared folders or printer. This time we don't even get set up to begin with, it just won't see anything. Internet access is fine.

I tried an Ethernet cable on the 360 and it worked flawlessly. I then tried dropping to WEP security as this was used on my old router. Hey presto, the laptop can see shared folders/printer and the 360 finds the media every time.

I would prefer to use WPA but it seems to take away some important functionality away from the router!

Any ideas what the problem could be?? (pc/laptop has all updates and upnp is enabled)