NuGet pack Unable to cast object of type 'System.String' to type 'NuGet.Frameworks.NuGetFramework Came across a rather misleading error message above today while attempting to pack and publish a .Net Standard class library project to a private feed as a DevOps Artifact. Well, it turns out that the NuGet Pack and NuGet Push are not supported by NuGet 4.x at this time. The workaround is to use the .Net core specific build tasks which include commands for pack and publish as show below: YAML -(PACK) steps: - task: DotNetCoreCLI@2 displayName: 'dotnet pack' inputs: command: pack packagesToPack: <your project.csproj> versioningScheme: byPrereleaseNumber -(PUSH) steps: - task: DotNetCoreCLI@2 displayName: 'dotnet push' inputs: command: push packagesToPush: '$(Build.ArtifactStagingDirectory)/**/*.nupkg;! $(Build.ArtifactStagingDirectory)/**/*.symbols.nupkg' publishVstsFeed: