TeamViewer: Not ready. Check your connection

Sometimes after switching the network connection (wired/wireless), TeamViewer service hangs.
To fix this - restart teamviewer service. Open a terminal and execute the following commands :

sudo teamviewer daemon stop
sudo teamviewer daemon start  

Alternatively you can restart the teamviewer service with : sudo teamviewer daemon restart
To check if the service was restarted successfully execute : sudo teamviewer daemon status

When it doesn't solve the problem, check if TeamViewer is blocked by the firewall of the router.
If you are working with an office system provided by a company, it may be blocked within there.

Additional information addressing the comments under the answer "Didn't work for me" :

Sometimes the installation of teamviewer by clicking the .deb file, which opens the Software Center, doesn't install the application including all required dependencies properly and hence fails.
Having installed and used TeamViewer successfully for many years, I can recommend to install TeamViewer by using the gdebi packaging tool, to install it execute sudo apt install gdebi. Right-click the .deb installation file and select to open it with gdebi - then start the installation.

Update December 2017 : TeamViewer 13 was released, for the first time as a native Linux client.
The installer added a TeamViewer repository which currently seems to be not correctly configured.
This may be due to the fact that TeamViewer 13 Linux is still only available as a preview edition. To avoid apt errors, I recommend to remove the repository and install new versions manually until the issue is fixed, to achieve this execute sudo rm /etc/apt/sources.list.d/teamviewer.list.

Update April 2018 : I've tested TeamViewer 13 on Ubuntu 18.04 LTS (running on Xorg) and the application installed correctly by clicking the .deb file. TeamViewer seems to work as expected.

Update August 2018 : TeamViewer 13 has left the preview state and became a regular product.

Update November 2018 : TeamViewer 14 was released and is being made available for Linux.

Users who experience problems with the new edition, may want to follow the discussions in the TeamViewer - Community TV General | Community TV Linux | Community TV TeamViewer 13.

It did get to work in my case by running below commands in a terminal:

    sudo systemctl stop teamviewerd.service

    sudo systemctl start teamviewerd.service