peter,
What are the versions of Arc Hydro data model (& ArcGIS) that you are using?
My adivices are, in order to fix:
1. check with Arc Hydro web for the latest data model and documentations. ArcHydro Tutorial and Documentation
2. Nice to contact Esri Water Resources Team, including the discussion at Ask Our Experts | GIS for Water Resources
To access for download, select a FTP client:
1. Web Client
Site link: https://mft.esri.com
(Video tutorials available on the main page, prior to log in)
2. Third party SFTP client
** Download a preconfigured client
https://mft.esri.com/EFTClient/Account/mft.zip **
3. FTP address to configure a third party SFTP client of your choice:
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Port: 22