EPANet dll integration in ArcMap Addin not working?

I am unable 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?