I am using Teamviewer 13 and have been successfully for sometime. Overnight a connection problem has materialised. On trying to connect to the main PC, am getting 'The Unable to Connect' message. The PC can connect to other devices but cannot receive. I have tried the normal reboots and switching off the computer on several occasions but this has not brought an improvement. If it helps the problem started with the PC stating that another version of Teamviewer was running when in fact nothing was open. I would be grateful for your assistance.
Close all Teamviewer session, Open Services look for the Teamviewer and stop the service and start. This resolved the issue for me on a couple of machines, two other i had to reinstall Teamviewer i am still not sure what caused it.