Fatal Error C1107

could not find assembly 'file': please specify the assembly search path using /AI or by setting the LIBPATH environment variable

A metadata file was passed to a #using directive that the compiler was unable to locate.

LIBPATH, which is described in the article for #using, and the /AI compiler option allow you to specify directories in which the compiler will look for referenced metadata files.

This error can occur when you retarget a project to use the Visual Studio 2022 toolset. Projects created by older versions of the toolset set properties TargetRuntime=Managed and TargetFrameworkVersion=4.0 by default. Starting in Visual Studio 2022, .NET Framework 4.0 isn't installed, and projects default to TargetRuntime=Native.

If you retarget a project that used /clr for some or all of its source files, starting in Visual Studio 2022 you must set certain properties to build your project. If all the source files in your project are compiled as managed code, use the /clr compiler option for your project. If only some files in your project use /clr, set the ManagedAssembly=true property in your project properties.

To set these properties in the IDE, open the Property Pages dialog for your project. Select the Configuration Properties > Advanced page.

• To set /clr for the entire project, change the Common Language Runtime Support property. You may also need to set the .NET Target Framework Version property. Choose Okay or Apply to save your changes.

• If you only use /clr for some of the files in your project, set the Enable CLR Support for individual files property to Yes. This value sets the ManagedAssembly=true property in your project properties. Choose Okay or Apply to save your changes.

For more information about the options on the Advanced property page, see Advanced Property Page.