When I activate online, a message says "Cannot connect to activation server"?

Explanation: 

If you are not experiencing any sort of strange issue with your web browser, your proxy server settings could be the one responsible for this error.

Here are two solutions:

Solution 1:
1. When “Network Error” dialog pops up, click "Advanced Options"
2. Choose "HTTP", input your IP, proxy server port, username and password, then click OK
3. Try to activate again

Solution 2:
1. Run IE and choose “Tools > Internet Settings” (or other browser's counterpart)

2. Choose "Connections" and click "LAN Settings"

3. Choose "Use a proxy server for your LAN" and input IP and port

4. During the activation, a dialog will prompt you to enter username and password. Complete it and finish the online activation

Note: If you cannot connect to the Internet, you should choose offline activation.