If you are experiencing a multitude of errors stating that types do not exist or that you need to add references that are already present, it’s possible that there may be a deeper issue with your project configuration or dependencies. Here are some steps you can take to troubleshoot the problem:

1. Verify .NET Framework version: Double-check that your project is targeting the correct .NET Framework version (4.6) by right-clicking on the project, selecting “Properties,” and navigating to the “Application” tab. Ensure that the target framework is set to “.NET Framework 4.6” or a compatible version.
2. Check web.config file: In a web project, the web.config file plays a crucial role in configuring the project. Ensure that the web.config file is properly configured and references the correct assemblies and namespaces. Look for any missing or incorrect configurations that could be causing the errors.
3. Check references and packages: Verify that all the required references and packages are correctly added to your project. Right-click on the project and select “Manage NuGet Packages.” Ensure that all the necessary packages are installed and up to date. Additionally, check the “References” section under your project in the Solution Explorer and ensure that the required assemblies are referenced.
4. Check project files: Make sure that all the required project files, including the .csproj file, are intact and not corrupted. You can open the .csproj file in a text editor to inspect its contents and ensure that the necessary references and settings are present.
5. Clean and rebuild: Perform a clean build of your project by right-clicking on the project and selecting “Clean.” Then, rebuild the project by right-clicking on the project and selecting “Rebuild.” This helps to eliminate any cached or stale build artifacts that may be causing conflicts.
6. Restart Visual Studio: Sometimes, Visual Studio may encounter issues that can be resolved by simply restarting the IDE. Close Visual Studio completely and reopen it to see if the errors persist.
7. Consider updating or reinstalling Visual Studio: If the above steps don’t resolve the issue, it’s possible that there may be an issue with your Visual Studio installation. Try updating to the latest version or reinstalling Visual Studio to ensure you have a clean and up-to-date environment.

If you’ve tried these steps and are still encountering errors, it may be helpful to provide more specific information about the errors you’re facing, along with any relevant code snippets or error messages.