Even with the final update, users encounter issues. Here are solutions specific to the 10.8 environment.

This is a 64-bit vs 32-bit registry issue. The HEC-GeoRAS installer is 32-bit. Manually copy the extracted files from C:\Temp\HEC-GeoRAS_Installer to C:\Program Files (x86)\ArcGIS\Desktop10.8\bin\ .

This is a .NET threading error. Ensure your map is in Layout View , not Data View, before writing the geometry. The final patch for ArcGIS 10.8 partially mitigates this.