My problem started after creating a custom control and drag and drop it to the toolbox palette for use it in design forms. First appeared a warning saying that there was a redundance between the custom control source file (.cs) and the projects executable (.exe). On executing/debugging appeared the error: unable to access the (.exe) because it's being used (and it was true).
A literally removed the whole source code regarding the custom control and last problem never stopped, until I checked out the references and it was referencing itself in order to be "able to" get the former custom control. I removed the reference and done!!
So: just check the references and remove the self-reference to the project.
