Hi John,
This may have something to do with the design stage your corridor is set to. I tested it with a design stage 7 - Final Linear Features, and the design surface did not appear (similar to your screen shot). This is because if the design stage is only showing linear features, there is no terrain mesh for the End Area Volumes command to pick up. There are just lines. I suggest setting it to a design stage with a mesh. If this is not the culprit, please post your dgn and the specific version number. I'll take a look at it.
Please take a look at this link that explains it as well: http://communities.bentley.com/products/road___site_design/f/5922/p/114812/352007#352007