I'm trying to make an elevation profile with QGIS's Profile from Line plugin. But when I do, the resulting points all have the same value: -32,767. I'd like to know what I'm doing wrong.
My elevation data is from GeoBase.ca (at 1:50,000 scale). My route line is selected in yellow, below.
As an aside: my route covers two raster files, and I haven't figured out how to render them to the same elevation scale. The top of the map is coloured as low elevation because of mountains to the north. I don't think this is the source of my problem -- when I sample the elevation layers with the Identify Features tool, it reports the elevation changes that I'd expect.

Here are the options I used with the Profile from Line tool:

Profile from Line makes a new layer. Here is its attribute table. Note that all of the values are the same.

What should I do to get a valid elevation profile? Thanks.