Compatibility issue between Visual Studio versions

Is everything good? I am having a compatibility problem with Versions 12 and 15 of Visual Studio. Come on. I created an ASP frontend project in Visual Studio Pro 12, a very extensive and complex project. I recently upgraded the version of my IDE to Visual Studio Pro 15 (both versions are original), and since then, when I run tests on my ASP page, the browser shows me "CONNECTIO REFUSED". I tried to use VS12 again to see if the error was in the project, but the same does not occur in version 12. When creating a new project in VS15, the error does NOT occur. I've already researched topics about file portability and differences in versions, but I have not found any reports of the same error yet. The project is accessed by the network, since it is inside a server. The error does not occur when using the product ready on another machine, it only happens when I run the test inside the IDE. If anyone has any idea of what might be happening, I would be grateful. Great day for you developers.