FYI,
I've been getting the same error and it's starting to drive me nuts. I know where the BasinHeader table is, it's added to the map, I've opened it to verify that it's real, and I specified the location of it using the Data Management tool in the GeoHMS toolbar. Still get the same error every time, and as a result I need to manually input the geometry information in HEC-HMS. Kinda defeats the purpose of using the toolbar.
So any updates from someone with a fix are still welcome.
Thanks
GH 12/12/2013
Using version 10.1