Arc Hydro Pro Identify Flat Areas Error

[MollyMuscato]

Hi, 

I'm in the process of creating flood depth rasters for a DEM with the goal of using the rasters to run the Flood Impact Analysis Solution on ArcGIS. Every time I attempt to run the "identify flat areas" tool, using the DEM data, I receive the following error message: 

I was wondering if anyone had any insight to what might be causing the tool to fail. I was concerned that it might be due to the size of the dataset as I'm looking at elevation data for an entire county. 

Thank you so much!