FileNotFoundException for IronXL.XmlSerializers on .NET 10

Curtis Chau

Updated: August 21, 2026

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  # FileNotFoundException for IronXL.XmlSerializers on .NET 10 Calling `WorkBook.SaveAs()` in a .NET 10 project can surface a `FileNotFoundException` for `IronXL.XmlSerializers` in Visual Studio. In most cases this is a first-chance exception caught by the debugger, not a real runtime failure, and the Excel file is still generated. ```txt FileNotFoundException: IronXL.XmlSerializers ``` The message comes from .NET XML serialization, which probes for an optional serializer assembly that is not present. IronXL handles that internally, but with **Just My Code** disabled the debugger breaks immediately on an exception the library already catches, making a harmless first-chance event look like a crash. ## Solution ### 1. Reproduce with a minimal workflow Create a new ASP.NET Core Web Application targeting .NET 10 and install `IronXL.Excel` 2026.6.1. ```xml <PackageReference Include="IronXL.Excel" Version="2026.6.1" /> ``` Then run a basic save: create a workbook, write `Hello, World` into cell `A1`, and save the file as `.xlsx` to your output path. ### 2. Enable Just My Code When an exception appears in Visual Studio, check the **Just My Code** setting under the debugger options. Enable it so the debugger stops breaking on exceptions that the library handles internally. ### 3. Confirm the file was generated Check whether the `.xlsx` file exists at your output path. If it does, you are looking at a first-chance exception break in the debugger, not an actual runtime failure. ## Notes - A first-chance `FileNotFoundException` related to .NET XML serialization can appear even when file generation succeeds. - There is no standalone `IronXL.XmlSerializers` NuGet package. Do not attempt to add one to resolve the message.

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Calling WorkBook.SaveAs() in a .NET 10 project can surface a FileNotFoundException for IronXL.XmlSerializers in Visual Studio. In most cases this is a first-chance exception caught by the debugger, not a real runtime failure, and the Excel file is still generated.

FileNotFoundException: IronXL.XmlSerializers

FileNotFoundException: IronXL.XmlSerializers

The message comes from .NET XML serialization, which probes for an optional serializer assembly that is not present. IronXL handles that internally, but with Just My Code disabled the debugger breaks immediately on an exception the library already catches, making a harmless first-chance event look like a crash.

Solution

1. Reproduce with a minimal workflow

Create a new ASP.NET Core Web Application targeting .NET 10 and install IronXL.Excel 2026.6.1.

<PackageReference Include="IronXL.Excel" Version="2026.6.1" />

<PackageReference Include="IronXL.Excel" Version="2026.6.1" />

Then run a basic save: create a workbook, write Hello, World into cell A1, and save the file as .xlsx to your output path.

2. Enable Just My Code

When an exception appears in Visual Studio, check the Just My Code setting under the debugger options. Enable it so the debugger stops breaking on exceptions that the library handles internally.

3. Confirm the file was generated

Check whether the .xlsx file exists at your output path. If it does, you are looking at a first-chance exception break in the debugger, not an actual runtime failure.

Notes

• A first-chance FileNotFoundException related to .NET XML serialization can appear even when file generation succeeds.
• There is no standalone IronXL.XmlSerializers NuGet package. Do not attempt to add one to resolve the message.

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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