See link: Easy Linux Tips Project: How to solve internet connection problems
Instructions:
disabled wifi card power saving to stop this error:
When Power Management is on, proceed as follows:
c. Use copy/paste for transferring the following blue line into the terminal (don't try to type it!):
sudo sed -i 's/3/2/' /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf
Press Enter. Type your password when prompted. In Ubuntu this remains entirely invisible, not even dots will show when you type it, that's normal. In Mint this has changed: you'll see asterisks when you type. Press Enter again.
d. Reboot your computer.
e. Then check in the terminal, by the command iwconfig, whether Power Management for the wireless chipset is off now.