I have a solution with 10+ projects (VS2010 SP1). I have the following configurations defined in the solution:
Here's a workaround if already checked the Create new solution configurations checkbox:
- Open Explorer and navigate to the location of the solution for the project that is missing platforms.
- Move the solution .sln file to a temorary location where Visual Studio won't locate it.
- Open the .csproj file for the project that is missing platforms.
- Click the Solutions Platform dropdown.
- Click Configuration Manager...
- In the table, Click the dropdown in the Platform column for the project and select , to add a new platform.
- Click OK.
- Repeat adding new platforms as needed.
- Save the project.
- Return the previously moved solution file back to where it was.
- Reopen the combined project solution.
source: https://developercommunity.visualstudio.com/content/problem/972/adding-a-platform-when-one-with-the-same-name-alre.html