You must first define the configurations in the Configuration Manager. To be sure you are bringing up the Configuration Manager, you can access it by going to: Build->Configuraton Manager
In the Active Solution Configuration dropdown, select <New...>. Once you've added, you will then be able to "Add Config Transform".
Don't edit your solution file directly. It will only cause headaches.

You must first define the configurations in the Configuration Manager. To be sure you are bringing up the Configuration Manager, you can access it by going to: Build->Configuraton Manager
In the *Active Solution Configuration* dropdown, select `<New...>`. Once you've added, you will then be able to "Add Config Transform".
Don't edit your solution file directly. It will only cause headaches.