Once you have chosen the .IFO file this is what appears.  As you can tell, Traffic is 2 hours and 27 min.  If you choose the wrong .IFO file, the duration will be something like 27 min.  You know that no movie is 27 min so, try the next .IFO file till you find the one that seems right.  Then click on the little green arrow.

 

 
This is what It looks like once you load the .IFO.  No real big screenshot here, just make sure the job size that is circled is a huge file.  If it is not, you may end up encoding the previews or trailers by accident.