This error is mostly causes because you did not select an option in the TT-store-setup.
Before you can use the plugin you have to select if you want to use the basic or the advanced version of the plugin. You can do that by following these steps:
1) In your wp-admin you will see TTstore on the left side (some where near the bottom)
2) When you click on TTstore you will get the setup tab. Here you can select between Basic and Advanced.
3) Select any of the 2 options and click on save. You will now see that the extra tabs will appear in your screen and you are able to setup the plugin.
If you still have the same issue after these steps please let me know the address in your address bar where you get that message and tell me how you went to that address (what link did you click on)