I have this exact problem! I have been trying multiple "workarounds" that I could think of, but nothing has worked. I've rebuilt the data in ArcMap 10.1, then ported it to Hec-Ras through the GEORAS extension, where everything works correctly. Then I get hit with the error you are having! If anyone has a fix for this, I, along with others, would be greatly appreciative.
Thanks,
DB