How Do I Fix the 'Could Not Load File or Assembly' Error in My .NET Application?

Solving the "Could not load file or assembly" Error: A Practical Guide

The dreaded "Could not load file or assembly, or one of its dependencies" error can be frustrating. This guide provides a systematic approach to diagnosing and fixing this common .NET issue.

Pinpointing the Problem Assembly

The error message usually names the problematic assembly. For example, it might point to Microsoft.Practices.Unity, Version=1.2.0.0. However, the root cause might be a dependency issue, not the assembly itself.

Examining Dependencies

Assemblies rely on other assemblies. A missing or outdated dependency is a frequent culprit. Ensure all assemblies referencing Unity use the correct version (e.g., 2.0.414.0) as defined in your project's .csproj files.

Removing Obsolete Assemblies

References to older Unity versions (like 1.2.0.0 in this example) can trigger the error. Thoroughly check your solution's .csproj files to eliminate any references to outdated assemblies.

Cleaning the Output Directory

Your project's output folder might contain outdated assembly versions. Inspect the output folder for any Unity assemblies with version 1.2.0.0 and remove them.

Leveraging FusLogVw

The Assembly Binding Log Viewer (FusLogVw) tracks assembly loading. Run FusLogVw while executing your application to pinpoint the assembly loading the incorrect Unity version. Double-clicking the first log entry reveals the calling assembly.

Further Troubleshooting Steps

• Rebuild the Solution: A complete solution rebuild ensures all assemblies are current.
• Clean and Rebuild: Cleaning and rebuilding the affected project can resolve temporary build issues.
• Assembly Binding Redirects: Check your configuration file (app.config or web.config) for custom assembly binding redirects.
• Dependency Injection: Consider using a dependency injection framework (like Unity itself) to manage assembly dependencies more effectively.

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