This was driving me nuts. It happened after an upgrade. Downgrading only partially solved the issue. It was working fine before the upgrade and the very act of upgrading seemed to break Team Viewer. I tried all the suggestions in the multiple threads over the years with issues similar to this. Nothing seemed to solve the problem. I tried disasbling my firewall, but Team Viewer itself is sensitive to and has problems with an unfirewalled machine. An intermin solutiuon was to TeamViewer into a computer that worked, which hadn't been upgraded, and then from there, TeamViewer LAN into the machine that stopped connecting to others as well as refused connections from anywhere besides LAN. However, that just seemed to be a very poor fix and often I would get confused as to which machine I was addressing. In turns out I found a solution that worked for me, In the proxy settings, default is "Automatic". However, I don't use a proxy. Even though my other installs (which weren't upgraded) had no problem with the default Automatic setting, checking the "no proxy" box on the problematic machine cleared everything up. This was 15 minutes ago, maybe tomorrow I"ll come back with a statement saying how upgrading TeamViewer broke itself again and that downgrading didn't fix it. However, I now have all my machines set to not automatically upgrade and at this point, I am very hesitant to upgrade any machine moving forward.
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