Cannot add folder <name>. An item with that name already exists.

You tried to add a folder to a Web project or to a database project, and the folder has the same name as a folder already in the project. For example, whenever you add data connections or database objects to a database project, the objects are added as folders and files in the database project.

• To correct this error, rename the object you're trying to add to the project.

  -or-

  Rename the folder already in the project.

For more information, see Reorganizing Project Structure.