Azure Pipelines · .NET Framework · Checked November 6, 2026

Azure Pipelines: MSB3644 "The reference assemblies for .NETFramework were not found"

To build a .NET Framework project, MSBuild needs the reference assemblies, the targeting pack, for that project's framework version on the agent. When the version is not there, the build stops with MSB3644. Microsoft-hosted Windows images come with packs for some versions only, and the Windows Server 2019 image, which many answers suggest, was retired on December 31, 2025 (Microsoft's page on hosted agents). Questions on Stack Overflow with this error in Azure DevOps have been seen over 140,000 times.

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What it looks like

• error MSB3644: The reference assemblies for .NETFramework,Version=v4.6.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application.
• In the .NET Core task, it comes before Dotnet command failed with non-zero exit code; in the Visual Studio Build or MSBuild task, before Process 'msbuild.exe' exited with code '1'.

Which versions the hosted images have

From the Visual Studio components listed in each image's readme in the runner-images repository, which Azure Pipelines uses too:

• windows-2022 and windows-2025 (today also windows-latest): 4.5.2, 4.6, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8 and 4.8.1.
• windows-2025-vs2026: 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8 and 4.8.1, so no 4.5.2 and no 4.6. Microsoft says windows-latest will point to this image, and that windows-2025 will also move to Visual Studio 2026. A 4.5.2 or 4.6 project that builds on windows-latest today will then hit MSB3644.
• On none of them: 4.0, 4.5, 4.5.1 and 4.6.1, the version in the most common question.

Reference assemblies from NuGet

• The Microsoft.NETFramework.ReferenceAssemblies package brings the reference assemblies with the build, for .NET Framework 2.0 up to 4.8.1, so the agent needs no targeting pack. Add <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3" PrivateAssets="All" /> to the project and restore before the build; this works for classic projects as well as SDK-style ones (the package's readme). A project that still uses packages.config has to move to PackageReference first.
• An SDK-style project built with the .NET SDK gets this package by itself when the pack is missing, so MSB3644 comes mostly from classic projects, built with the Visual Studio Build or MSBuild task.

A newer target framework

• Support for .NET Framework 4.5.2, 4.6 and 4.6.1 ended on April 26, 2022 (Microsoft's announcement), which is why images drop them. Retargeting the project to 4.6.2 or later, ideally 4.8 or 4.8.1, makes it build on every hosted image, but is a change to test, not only to the build.

A self-hosted agent

• On your own agent, install the developer pack (or targeting pack) for the version, from Microsoft's .NET Framework downloads or with the Visual Studio installer, and restart the agent.

'.NETFramework,Version=v5.0'

• A version 5.0 or later in this message means a .NET 5 or later project is being built by an MSBuild or NuGet too old to know it, which reads net5.0 as .NET Framework. The accepted answer on the question about it: install the SDK with UseDotNet@2 and build with the .NET Core task.

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