I have microsoft visual studio 2015 pro, and arcgis 10.5 and arcobjects sdk .net 10.5 on my computer with windows 10 home. I can create a new project from Visual C#, ArcGIS, Extending Arcobjects (class library arcmap) without any problem. But whenever I try to add my project to a new class from ArcGıs extending arcobjects (such as toolbar), I am getting error like "a file with the name 'blabla.cs' already exist or is open an editor.Please .....". I am sure that my folder did not include such a class file I created before. What is missing or wrong about my system and what should I do in order to not get such an error again?