I am in trouble to get EPANet dll function running from my ARCMap Addin (C#.NetAPI). The same source for dll's function calling is working in an independent console application but when I do the same calling from ArcMap Addin button click, it returns error 305 which means “Cannot open hydraulics file” . But I do not understand why ArcMAP calling causes to stop creating/ accessing this file. I also tried to run the same console executable in a different process (started from ArcMAP Addin button even), but still no luck. Do anyone of you have any clue regarding this matter?