Assembly Mismatch After Version Upgrade in .NET Framework

Updated:June 9, 2026

After upgrading IronPDF in a .NET Framework project, the application throws this exception at runtime:

System.IO.FileLoadException: Could not load file or assembly 'IronPdf, Version=X.Y.Z.W,
Culture=neutral, PublicKeyToken=...' or one of its dependencies. The located assembly's
manifest definition does not match the assembly reference.
(Exception from HRESULT: 0x80131040)

The NuGet package upgrade installs new assembly versions, but the old versions remain cached in the project's bin/Debug (or bin/Release) and runtimes output directories. .NET Framework resolves assemblies from these local folders before consulting the NuGet cache, so the stale cached DLLs conflict with the newly installed package and cause the binding failure.

Solution

Step 1: Uninstall IronPDF and all Iron-related packages (such as IronPdf.Slim, IronPdf.Native.Chrome.Windows) using NuGet Package Manager in Visual Studio (Tools > NuGet Package Manager > Manage NuGet Packages for Solution).

Step 2: Delete the runtimes folder and the bin/Debug (or bin/Release) folder from your project output directory.

Step 3: Reinstall IronPDF via NuGet Package Manager.

If Visual Studio cleanup is insufficient, clear the global NuGet cache via the command line and force a clean restore:

dotnet nuget locals all --clear
dotnet restore --force

dotnet nuget locals all --clear
dotnet restore --force

SHELL

For server deployments: remove all old IronPDF DLLs from the server directory before republishing. Deploy to a fresh directory and update IIS to point to the new location rather than overwriting files in place.

Curtis Chau

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Technical Writer

Curtis Chau holds a Bachelor’s degree in Computer Science (Carleton University) and specializes in front-end development with expertise in Node.js, TypeScript, JavaScript, and React. Passionate about crafting intuitive and aesthetically pleasing user interfaces, Curtis enjoys working with modern frameworks and creating well-structured, visually appealing manuals.

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