I wrote several WPF interfaces and found no problems when using AddinManager. However, when compiled into an addin file and packaged, it reported an error:
Could not load file or assembly “Microsoft.Xaml.Behaviors, PublicKeyToken=b03f5f7f11d50a3a” or one of its dependencies

After modifying it many times without success, I remembered that Revit cannot load strong-named dll files, so I replaced it with a package that has stopped maintenance:
System.Windows.Interactivity
It runs normally after packaging.

If we use nuget to search for the package of interactivity.dll, it will prompt that there is a new package available for download. If you use this package for Revit secondary development, you should use this dll that has stopped maintenance updates.

![Image Description](https://cdn.bimath.com/blog/pg/Snipaste_2026-01-04_16-56-53.png)