Can't change target platform to "any CPU"

Solution 1:

In the configuration Manager, you can add a new platform for your project. However, you need to uncheck the "Create new solution platforms" if you already added the platform for your solution, otherwise you will indeed get the warning that the solution platform is already there.

Solution 2:

To change target platform do the following:

[1.] Open the configuration manager

[2.] In platforms, select new.

[3.] New platform select x64 or you need, in "copy settings from" select "Any CPU" or "Empty", and uncheck the "Create new solution platforms"

source: ericklan.com

Solution 3:

You can proceed as follow to configure the target platform:

1. In Visual Studio, right click on the solutionSelect "Properties"
2. A setting dialog will appear
3. Click on configuration Settings: You will see all the projects of the solution and the configation of the compilation.
4. Click on "Configuration Manager" button (top right of the dialog)
5. You will see two dropdowns, click on the "Target Platform" one and then on "New" in order to add the the desired target platforms
6. Once the desired target platforms added, choose the one that you want
7. Click close then Ok