I had this same behaviour a couple days ago. I think it was because there were some blocks near the front of the controller (opencomputers stuff). Any chance its the same in your case?I am having a strange behavior, i made a diesel engine before, but not it shows the "incomplete structure" , and i did not touched it, i even removed all the blocks and replaced them just like the book says but it still dont form. help?
After I removed the blocks, it took a few seconds but then the incomplete-structure message went away.