Fabio1 Thank you.
I would recommend re-creating the project so it's a new project type. The old one is not well supported by the new Visual Studio, and causes performance issues, especially in combination with TFS.
Go to File -> New -> Project, and look for "PHP Project from Existing code"
, and recreate the project file in your existing project directory.
Please let me know if it helps, or if you'd need more help with it.
Thank you