http://forum.tp-link.com/showthread.php?4310-Failed-to-switch-wireless-network-adapter.&region=china

seen by you already. That's the answer why you can't switch because you only installed one wireless adapter.

Hi guys, did you manage to find a solution? I have the same problem!
Simon, the current state is no adapter selected.

Additional information: I have an internal Atheros wifi card on my HP laptop. I thought it was broken so I tried to replace it with a stick, but sounds exactly like the above situation.
Also, I'm in Australia with a TL-WN821N stick...

Thanks!
Kent

Ok,

I worked on this all day and got the fix.

I have a TL-WDN4800, I installed the hardware and I used the cd that came with the product, clicked on autorun and followed the instructions by installing the driver and utilities.

No wireless networks would come up. The device manager said all was good.

Windows Server 2008 R2 (Pretty sure the fix is OS universal)

THE PROBLEM IS I did not have WLAN AutoConfig running.

So Installed the service, but it still did not appear to work just magically. I rebooted out of habit.

Then I followed the instructions here. http://www.tp-link.com/en/faq-306.html

Mind you! NO wireless networks were showing up at the time.

After I did a "Manual" "Connect to network the wireless networks showed up and I clicked on my 5g network and its all good.

Hope this helps.

Cheers!

DL