How about posting a sample file that contains ALL of the data entry lines that are required for the Import HEC-RAS function to do so without error(s). At least a user would then have something (documented) to compare their bad file against, and at the very least be able to enter or create the data lines required for success during import.
We may not be able to see a fix for this, and in the interim it would at least give a template of what data the applet wants and the format it desires.