If you have certain third-party apps downloaded, such as screen filters, battery savers, or launching apps, they may interfere with your ability to select the 'I trust this application' checkbox. Some of these apps include Twilight, Rotation Manager, Dodol Launcher, and Juice Defender. Turning these applications off briefly will allow you to select this checkbox. Once that is done, you can turn those apps back on, and TunnelBear should function properly.