Question: I have installed Visual Studio 2022 on my PC today. I have an old app, which targets .NET 4.5. I see this error when attempting to build/compile the project:

"Error MSB3644 The reference assemblies for .NETFramework,Version=v4.5 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at [https://aka.ms/msbuild/developerpacks"](https://aka.ms/msbuild/developerpacks%22)

I have read this: <https://thomaslevesque.com/2021/11/12/building-a-project-that-target-net-45-in-visual-studio-2022/>. C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework.NETFramework\v4.5 already exists on my PC.

I have downloaded the .NET 4.5 Developer Pack here: <https://learn.microsoft.com/en-gb/dotnet/framework/install/guide-for-developers>. I see this when I attempt to run it:

[![enter image description here](https://i.stack.imgur.com/5PtsJ.png)](https://i.stack.imgur.com/5PtsJ.png)

Is there anything else I can try?

Answer: 
Because you might install a higher version of .net framework firstly, so installer might stop you install a lower version of .net framework

There is another way can try to fix it without reinstalling.

1. Download [Microsoft.NETFramework.ReferenceAssemblies.net45](https://www.nuget.org/packages/microsoft.netframework.referenceassemblies.net45) package file
[![enter image description here](https://i.stack.imgur.com/DaWmb.png)](https://i.stack.imgur.com/DaWmb.png)
2. Modify the file extension name from `microsoft.netframework.referenceassemblies.net45.nupkg` to `microsoft.netframework.referenceassemblies.net45.zip` and Unzip that
3. Copy the files from `build\.NETFramework\v4.5\` to `C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5`
4. Running your project again.

**Note**

This way was also work for .net4.0 [Microsoft.NETFramework.ReferenceAssemblies.net40](https://www.nuget.org/packages/Microsoft.NETFramework.ReferenceAssemblies.net40/) or other [older version of .net framework](https://www.nuget.org/packages?q=Microsoft.NETFramework.ReferenceAssemblies) which Microsoft might not support in feature
If you want a less hacky way, another option is to download the VS2017 Build Tools and install the .NET Framework 4.5 Targeting Pack only (from the tab Individual Components). This works fine with Visual Studio 2022, since it installs the reference assemblies where they are needed.

[![enter image description here](https://i.stack.imgur.com/YGVcI.jpg)](https://i.stack.imgur.com/YGVcI.jpg)