Hello,
I have been using TeamViewer Free for a while now and since I upgraded to V12 I have been getting this error.

Before this I was using V11 and had no issue with this.
This is what my TeamViewer looks like on both computers and note that it says Free version.
Computer 1
Computer 2

A couple of Notes: When I do the installation I make sure I'm checking "For personal use Only"
I used to use a licenensed version for a client on one of my computers a while ago using V8 and V9. Since then I only use TV for personal reasons on a different account.
The flag is for Low disk space on one of my computers.