I'm clearly not an expert but have been using Arc Hydro and Geo_HMS in Arcmap 10.4.1 fairly successfully for several years. Last Friday (5/24) I suddenly started getting a new error message "System.Runtime.InteropServices.ComException (0x80004005): Error HRESULT E_FAIL has been returned from a call to a COM component at ESRI.ArcGIS.Geoprocessing.GeoProcessorClass.Execute(String Name, ..." in DEM reconditioning. I looked up the available solutions online and none of them fixed the problem. I tried old projects which had worked perfectly in the past and received the same error message. Everything was fine on Thursday and DOA on Friday. I couldn't imagine what I had done wrong. I next upgraded to Arcmap 10.6.1 (adding all of the patches) but still got the same error. I'm stuck. My mistake should be so obvious that it's smacking me in the face but I can't see it. Any thoughts?