"BOAT CHANGE" for me, I'll be using the U-56 Dunlop Motorsports.

TJ Czerwinski U-56 Miss Mossy Oak

Sounds like you may have pulled the HydroSim.exe out of the folder group for an easy access shortcut, not sure, but it's been done by a few. That error message will show up if you do that, the HydroSim.exe must be opened in the folder group. Re-download and overwrite it again and try opening the HydroSim.exe where you find it, don't move it. you can always pull the whole group to the desktop if needed.