Configuration With Same Name Already Exists

Question

Make sure you're using the drop down list from the grid (not the one at the top of the dialog), and do not check the "Create new solution configurations" checkbox when adding your new project configuration.

Here's a workaround if already checked the Create new solution configurations checkbox:

1. Open Explorer and navigate to the location of the solution for the project that is missing platforms.
2. Move the solution .sln file to a temorary location where Visual Studio won't locate it.
3. Open the .csproj file for the project that is missing platforms.
4. Click the Solutions Platform dropdown.
5. Click Configuration Manager...
6. In the table, Click the dropdown in the Platform column for the project and select , to add a new platform.
7. Click OK.
8. Repeat adding new platforms as needed.
9. Save the project.
10. Return the previously moved solution file back to where it was.
11. Reopen the combined project solution.

source: https://developercommunity.visualstudio.com/content/problem/972/adding-a-platform-when-one-with-the-same-name-alre.html