The 5 Ghz WiFi support of the Flash Plus 2 is basically problematic.
The Flash Plus 2 can only connect to a few 5 Ghz Channels.. On my router it can connect if the router is set to Channels 36, 40, 44, and 48. It can not even detect the Wifi Network if the router is set to Channels 149, 153, 157, or 161.
I've tested a variety of other devices including about 6 different models of phones, 2 models of tablets, 2 laptops, and 3 wireless dongles and the only device unable to the previously mentioned channels is the Flash Plus 2. I doubt it is a problematic unit either as I have tested 6 different units of Flash Plus 2 (4 16GB and 2 32 GB) and they all exhibit the same problem.
If you have admin access to the router, then you can just adjust the channels accordingly. However, this is not always possible, you will not Admin Access to the routers of all the places you visit and I doubt that people will be so considerate as to switch their 5 Ghz channel for you just so that this one model of phone can connect to the WiFi network.
Hopefully this is just a software issue and can be fixed with an update. If it is a hardware issue then it is a certainly a major weakness of the Flash Plus 2 and it should be clearly stated on the specs sheet that the Flash Plus 2 that it only supports a few channels in the 5 Ghz wifi range.