Forget all that ^^.
I've just realised you said '.tgo files', sorry.
If your .tgo isn't opening images correctly, you need to: Open the .tgo in TG2, reassign all the shaders/images if required, visit the actual folder on your computer where the object is and delete it(you can delete files that are in use in TG already), lastly, re-save the object node as .tgo.
The new shader setup will be saved if you delete the original file, I find that the settings are the same as they were before upon reopening, if I don't delete the original .tgo first. I don't know why this is.