One thing to try is right-clicking the GTK-G app and choose Run as Administrator.
Failing this you might also try changing the program's compatibility mode to see if any such changes make a difference.

Note: I am not certain where GTK-G keeps the settings folder on Windows.
With uninstalling, did you also remove the program settings folder, it's often an option when uninstalling apps? That can sometimes fix certain issues such as if a file is corrupted or data within is corrupted.
START menu > type/copy-paste %appdata% (In theory this is where the settings folder should be.)
You should find GTK settings folder within. Though I have a suspicion GTK may hide it. In which case you would need to turn on Show Hidden Files & Folders in system settings. https://support.microsoft.com/en-us/...1-9b7f9840fdb2
But if you do this, then re-install the app because GTK-G pre-installs important data to allow the app to start and connect smoothly.