WPF control library's resource assembly not found at runtime despite being present in output directory (worked before system reinstall)

[yangf85]

Description

Environment:

• ExcelDNA Version: [latest version, no .dna file]
• .NET Framework: [net48 net8-windows]
• Excel Version: [exce2016]
• Visual Studio: [2022]
• Windows Version: [win10]

Problem:
I'm developing an ExcelDNA add-in that references a WPF control library via NuGet. This control library has a dependency on a style/theme resource assembly (Cyclone.Wpf.Themes).

Critical Information: This add-in was working perfectly before I reinstalled Windows. After the system reinstall, with the same code and project configuration, the add-in now throws a FileNotFoundException for the resource assembly.

Important: The Cyclone.Wpf.Themes.dll file IS present in the bin\Debug (or bin\Release) directory after building, sitting right next to the main add-in DLL and the .xll file. However, when the ExcelDNA add-in launches a WPF window at runtime, it throws a FileNotFoundException for this assembly.

Error Message:

System.Windows.Markup.XamlParseException
  HResult=0x80131501
  Message="设置属性"System.Windows.ResourceDictionary.Source"时引发了异常。"，行号为"3"，行位置为"10"。
  Source=PresentationFramework
  StackTrace:
   在 System.Windows.Markup.XamlReader.RewrapException(Exception e, IXamlLineInfo lineInfo, Uri baseUri)
   在 System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)
   在 System.Windows.Markup.WpfXamlLoader.LoadBaml(XamlReader xamlReader, Boolean skipJournaledProperties, Object rootObject, XamlAccessLevel accessLevel, Uri baseUri)
   在 System.Windows.Markup.XamlReader.LoadBaml(Stream stream, ParserContext parserContext, Object parent, Boolean closeStream)
   在 System.Windows.Application.LoadComponent(Object component, Uri resourceLocator)
   在 Cyclone.ExcelToolkit.Views.OrderDataFillView.InitializeComponent() 在 E:\Code\Cyclone\ExcelToolkit\Cyclone.ExcelToolkit\Views\Production\OrderDataFillView.xaml 中: 第 1 行

内部异常 1:
FileNotFoundException: Could not load file or assembly 'Cyclone.Wpf.Themes, Culture=neutral, PublicKeyToken=null'. 系统找不到指定的文件。

Project Structure:

ExcelDNA Add-in Project
├── References WPF Control Library (NuGet)
    └── WPF Control Library references Cyclone.Wpf.Themes (style/resource assembly)

Output Directory (bin\Debug):
├── MyAddIn.dll
├── MyAddIn.xll
├── MyAddIn-packed.xll
├── WpfControlLibrary.dll
├── Cyclone.Wpf.Themes.dll  ← THIS FILE EXISTS HERE
└── Other dependencies...

Steps to Reproduce:

1. Create an ExcelDNA add-in project using the latest NuGet package
2. Add a reference to a WPF control library that depends on a separate resource assembly
3. Build the project - verify that all DLLs including Cyclone.Wpf.Themes.dll are in the output directory
4. Create a WPF window that uses controls from the library
5. Launch the window from the Excel add-in
6. The FileNotFoundException occurs when the window tries to load resources, even though the DLL is physically present in the same directory

What Changed:

• Before system reinstall: The add-in worked perfectly with the exact same code and project structure
• After system reinstall: The FileNotFoundException occurs
• No code changes were made between the working and non-working states
• All Visual Studio, .NET Framework, and Excel versions were reinstalled to the same versions as before

Additional Information:

• The Cyclone.Wpf.Themes.dll IS present in the bin\Debug directory - this is not a build/copy issue
• The same WPF window works correctly in a standalone WPF application with the same DLL structure
• The issue only occurs when running as an ExcelDNA add-in within Excel process
• The resource dictionary is referenced in XAML like: <ResourceDictionary Source="/Cyclone.Wpf.Themes;component/Themes/Generic.xaml"/>
• Using Process Monitor shows Excel is not even attempting to load the DLL from the add-in directory

Expected Behavior:
Since all required DLLs are present in the output directory, and the add-in worked before the system reinstall, the WPF window should be able to load its resource assemblies when launched from the ExcelDNA add-in.

Core Questions:

1. Why can't WPF/XAML find the Cyclone.Wpf.Themes.dll assembly at runtime when running inside Excel via ExcelDNA, even though the file exists in the same directory as the add-in?
2. What system-level configuration or dependency could have changed after a Windows reinstall that would affect assembly loading in ExcelDNA but not in standalone applications?
3. Is there a Windows setting, GAC registration, or .NET configuration that ExcelDNA relies on that might not be properly configured after a fresh Windows installation?
4. Could this be related to security policies or trust levels that affect how Excel loads assemblies?