I was prompted to ask my partner to update her Team Viewer software when I tried to connect, and when I checked for updates, I noticed that my software was also out of date. So my partner and I both just updated our TeamViewer software. After downloading the latest version to my Mac, when I checked for updates, I got "You're up-to-date! TeamViewer 10.0.140455 is currently the newest version available." However, when I try to connect to my patner's PC, I get this message: "Your partner uses a newer version of TeamViewer. You need to update TeamViewer to establish a connection." This person is very computer illiterate (which is why I am trying to connect and help her). She's using a PC, and probably Windows 7. Not sure what to do next to fix this problem.
Probably W7 has a newer version. So, it is not possible to connect from older version to newer. It is only from her side with the reinstallation of the Team Viewer v.10 on her computer you has a chance to solve this issue. Try to guide her to reinstall the program. And give a link to download v.10 Team Viewer for W7, so she do not search it herself. Or send her a file with email, for example. Might this help.