Check the IP address of the wireless part. If the IP address is alright, try to change the DNS sever of the wireless network connection to 8.8.8.8 and see whether it works or not.

That is quite technical. But i heard that if the country is included within the country list of the access point, it should be OK to use in that country without violating the LAW. I can see Germany...

firstly make sure the router has been upgraded to the latest firmware. If it is already the latest one, try to use Connect on Demand with the connection type under 3G part.

I can not find that model on the TP-LINK website, that may be a customized product for some area. Maybe you can send an email to the Support requiring for the new firmware.:o

How about change the Wireless channel to a fixed number on the access point?

Make sure that the DHCP on the access point has been disabled. What's more, the network in your office should have the ability to issue an IP address to every new device connected. You know, if the...