Aha! That's a good clue. I was having upload trouble with a KML file created from Google Maps. (the procedure is: get directions; modify route manually; add &output=kml to the end of the URL; save resulting file).
I just did an experiment with a route from the White House to Gettysburg.
Here is KML file M, straight from Google Maps.
Here is KML file E, which I got by opening file M in Google Earth and then doing a "Save as KML". That is, E is just a version of M that I filtered through Google Earth.
If I browse and select file M, absolutely nothing happens when I click [upload]. On the other hand, if I browse and select file E, everything works normally and I can build the PQ.
I don't know what subtle difference is causing the two very similar KML files to behave differently, but maybe this is a good clue about the problems that some folks are having.
Thanks I tried it this way and got it to work!!