I am using Windows 7 (32-bit). I have Lync 2010 installed and it works fine on my office network (LAN - Wired) and in Wifi, but when I try to Sign in from USB dongle, it does no sign in and shows the error "The server is not responding or cannot be reached. Sign In may be delayed while we retry". 

I am able to connect VPN and outlook when my system is connected to USB dongle.

Please help me resolve this.

The network path is pretty much transparent to Lync, it's just trying to connect to the server.  Is the USB dongle just a USB network card?  See if you can ping sip.yourdomain.com and telnet to it on port 5061.  Also, confirm that you can resolve _sipinternaltls._tcp.yourdomain.com and get the appropriate records.

-Anthony

Hi,

Did you mean the computer will connect to the Lync Server with VPN when using a USB network card?

Please check when using the USB network card, the computer could directly to connect internal network or will through the Internet to internal network.

If yes, please check if there is any port block for Lync Server (such as port 443).

Best Regards