I also got the same error (Error initilizing TecSDK Failed to create instance of Tet extension) while trying to load the Tobii Showcase.
I simply needed to plug the device in and run through the initial profile setup first, then it worked.
I didn’t do that at first though, because most similar things prompt you when it’s the right time to plug the device in; often you are warned not to plug them in too early, before you have the drivers installed properly.
And the error message is far from user-friendly! (How about just saying, please plug it in?)