I received this error because I used the incredibly broken NuGet Package Manager in Visual Studio 2015 to update my project.json dependencies. It turned this:
"frameworks": {
"netcoreapp1.0": {
"dependencies": {
"Microsoft.NETCore.App": {
"type": "platform",
"version": "1.0.1"
}
}
}
}
into this:
"dependencies": {
"Microsoft.NETCore.App": "1.1.0"
},
"frameworks": {
"netcoreapp1.0": {}
}
Bye bye, platform definition!