Registering Extensions of the .NET Framework
You can develop an assembly that extends a specific version of the .NET Framework. To enable the assembly to appear in the Visual Studio Add References dialog box, you must add the folder that contains it to the system registry.
For example, assume that the Trey Research company has developed a library that extends the .NET Framework 4, and wants the library assemblies to appear in the Add References dialog box when a project targets the .NET Framework 4. Also assume that the assemblies are 32-bit assemblies running on a 32-bit computer or 64-bit assemblies running on a 64-bit computer, and that they will be installed in the C:\TreyResearch\Extensions4\ folder.
Register this folder by using this key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v4.0.21006\AssemblyFoldersEx\TreyResearch\. Give the key this default value: C:\TreyResearch\Extensions4.
The build number of the .NET Framework version may be different.
To register a 32-bit assembly on a 64-bit computer, use the Wow6432 node, for example: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v4.0.21006\AssemblyFoldersEx\TreyResearch\.