If it only concerned with the wireless network connection, you may try to fix the channel on the modem. Or give a try to upgrade the firmware, reset the modem and reconfigure it.

when you are configuring the virtual sever settings, make sure the port number, IP address, especially the Use Interface are correct. otherwise, you may do a DMZ for the camera's IP.

Probably you can delete a profile on the computer and reconnect the wireless to see whether it will work or not. for windows XP: http://www.tp-link.com/en/article/?faqid=186 for windows 7 and vista:...

As far as I am concerned, the 5GHz device cannot discover another device from 2.4GHz, if you have a 5GHz router, this adapter cannot be connected through 5GHz.

I tried the link you gave here, and it is working... Maybe you can try this one: http://www.tp-link.com/en/support/download/?model=TL-WR740N&version=V4#tbl_j

It seems no much difference between the two adapters, and there is no information on the web site. I guess maybe the compatibility has a little difference:)