Missing or corrupted dependencies

Oct 13, 2025 by wbrum.org 14 views

Introduction

Deploying an ASP.NET MVC 5 project to IIS can be a straightforward process, but sometimes it can lead to unexpected errors. One such error is the "Could not load file or assembly 'System.IO' or one of its dependencies" exception. This error can be frustrating, especially when you've tried various solutions from online resources. In this article, we'll delve into the possible causes of this exception and provide a step-by-step guide to resolve it.

Understanding the Error

The "Could not load file or assembly 'System.IO' or one of its dependencies" exception typically occurs when the .NET runtime is unable to load the System.IO assembly or one of its dependencies. This assembly is a fundamental part of the .NET Framework and is used for various file system operations. The error can be caused by a variety of factors, including:

Missing or corrupted dependencies: The System.IO assembly may be missing or corrupted, preventing the .NET runtime from loading it.
Incompatible .NET versions: If the project is targeting a specific .NET version, but the IIS server is running a different version, it can lead to compatibility issues.
Incorrect configuration: Misconfigured settings in the web.config file or the IIS application pool can cause the error.

Troubleshooting Steps

Before we dive into the solutions, let's review the troubleshooting steps you've already taken:

Clean and rebuild the project: You've tried cleaning and rebuilding the project to ensure that all dependencies are up-to-date.
Check for missing dependencies: You've checked for missing dependencies and ensured that all required assemblies are present in the project.
Verify .NET versions: You've verified that the project is targeting the correct .NET version and that the IIS server is running the same version.

Solution 1: Check the Web.config File

The web.config file contains critical configuration settings for the project. Ensure that the following settings are correct:

<system.web>: Verify that the <system.web> section is present and contains the correct settings.
: Check that the section is present and contains the correct settings, including the target framework version.
: Verify that the section is present and contains the correct settings.

Solution 2: Verify IIS Application Pool Settings

The IIS application pool settings can also cause the error. Ensure that the following settings are correct:

.NET Framework version: Verify that the .NET Framework version matches the project's target framework version.
Managed pipeline mode: Check that the managed pipeline mode is set to Integrated.
Application pool identity: Verify that the application pool identity is set to a valid user account.

Solution 3: Check for Conflicting Assemblies

Conflicting assemblies can cause the error. Ensure that the following assemblies are not present in the project:

System.IO: Verify that the System.IO assembly is not present in the project.
System.IO.Compression: Check that the System.IO.Compression assembly is not present in the project.

Solution 4: Rebuild the Project with the Correct .NET Version

If the project is targeting a specific .NET version, but the IIS server is running a different version, it can lead to compatibility issues. Rebuild the project with the correct .NET version to resolve the issue.

Solution 5: Use the Fusion Log Viewer

The Fusion Log Viewer is a tool that helps diagnose assembly loading issues. Use the Fusion Log Viewer to identify any issues with assembly loading.

Conclusion

The "Could not load file or assembly 'System.IO' or one of its dependencies" exception can be caused by a variety of factors, including missing or corrupted dependencies, incompatible .NET versions, and incorrect configuration. By following the troubleshooting steps and solutions outlined in this article, you should be able to resolve the issue and deploy your ASP.NET MVC 5 project to IIS successfully.

Additional Resources

ASP.NET MVC 5 Deployment Guide
Fusion Log Viewer
System.IO Assembly
System.IO Exception after IIS Deployment: A Q&A Guide ===========================================================

Introduction

In our previous article, we discussed the possible causes of the "Could not load file or assembly 'System.IO' or one of its dependencies" exception after IIS deployment. We also provided a step-by-step guide to resolve the issue. In this article, we'll answer some frequently asked questions related to this exception.

Q: What are the common causes of the System.IO exception?

A: The common causes of the System.IO exception include missing or corrupted dependencies, incompatible .NET versions, and incorrect configuration.

Q: How do I check for missing dependencies?

A: To check for missing dependencies, follow these steps:

Open the project in Visual Studio.
Right-click on the project and select "Manage NuGet Packages".
Check the "Installed" tab to see if all required assemblies are present.
If an assembly is missing, click on the "Browse" tab and search for the assembly.
Install the assembly and try to deploy the project again.

Q: How do I verify the .NET versions?

A: To verify the .NET versions, follow these steps:

Open the project in Visual Studio.
Right-click on the project and select "Properties".
In the project properties window, select the "Build" tab.
Check the "Target framework" dropdown to see the target .NET version.
Verify that the IIS server is running the same .NET version.

Q: How do I check the web.config file?

A: To check the web.config file, follow these steps:

Open the project in Visual Studio.
Navigate to the web.config file in the project directory.
Open the web.config file in a text editor.
Check the <system.web> section to ensure that it is present and contains the correct settings.
Check the section to ensure that it is present and contains the correct settings.

Q: How do I verify the IIS application pool settings?

A: To verify the IIS application pool settings, follow these steps:

Open the IIS Manager.
Navigate to the application pool that is hosting the project.
Click on the "Basic Settings" button.
Check the .NET Framework version to ensure that it matches the project's target framework version.
Check the managed pipeline mode to ensure that it is set to Integrated.

Q: How do I use the Fusion Log Viewer?

A: To use the Fusion Log Viewer, follow these steps:

Open the Fusion Log Viewer tool.
Click on the "Log" tab.
Select the log file that corresponds to the project.
Check the log file for any errors related to assembly loading.
Use the information in the log file to troubleshoot the issue.

Q: What are some common solutions to the System.IO exception?

A: Some common solutions to the System.IO exception include:

Rebuilding the project with the correct .NET version.
Checking for missing dependencies and installing any missing assemblies.
Verifying the IIS application pool settings and ensuring that they match the project's target framework version.
Using the Fusion Log Viewer to troubleshoot assembly loading issues.