Hi Stuart,
I am using ArcGIS Desktop 10.1 with the HEC-GeoRAS 10.1 toolbar.
I am attempting to delineate floodplains for 2, 10, 25, 50, and 100 year floods using a surface elevation raster GRID. The .gdb, bounding polygons, XS, etc. were created without error, as were the water surface TINs. The error occurs when I attempt to delineate the floodplain (resulting in a raster with cell values indicating water depth)