I started getting this warning in the help compiler log. I wouldn't care, but it is a very large help system and the warning causes a time-consuming re-compile every time:
HHC4006: Warning: The file "SolidWorks.Interop.sldworks~SolidWorks.Interop.sldworks.ISurface~ICreateTrimmedSheet3.html" is already listed in the [FILES] section of the project file.
I opened in notepad the dxc file that contained ICreateTrimmedSheet3 and searched for it. I found that the interface's properties (<item/>) had been moved to another location in the file, away from the interface <item/>. After I moved the property <item/>s to be directly under the interface <item/>, the warning went away.