Passing along a learned lesson.
I have upgraded my ArcPro to version 3 and have installed the newly available Arc Hydro 3.0.21. When I open an existing project created prior to ArcPro 3 and try to run any ArcHydro tools I get a "Tool has failed to open" message. This still occurs after saving the project under ArcPro 3.
However, when I start a new project with ArcPro 3 and try to run any Arc Hydro tool everything goes ok.
Lesson learned, after upgrading to ArcPro 3, any old projects created under ArcPro 2.x will not be able to utilize any ArcHydro tools.
Tom