Errors When Creating New VB or C# Projects After Installing Latest Application Version
Environment
| Product | Installer and VS Extensions/UI for ASP.NET AJAX |
| Version | 2026.3.812 |
Description
When creating new VB or C# projects using the Telerik Visual Studio extension, the following error occurs:
System.IO.FileNotFoundException: Could not load file or assembly 'System.Collections.Immutable, Version=9.0.0.0'This issue arises due to a mismatch between the Telerik Visual Studio extension's compiled dependencies and the runtime components available in the Visual Studio environment. The System.Collections.Immutable assembly version 9.0.0.0 is part of the .NET 9 SDK. If this SDK or its runtime components are unavailable, the extension fails to load the required dependencies.
Cause
The error occurs because the Telerik Visual Studio extension expects the System.Collections.Immutable assembly version 9.0.0.0, which ships with the .NET 9 SDK. If .NET 9 SDK is not installed or Visual Studio cannot resolve the required version, the assembly fails to load, resulting in the error.
Solution
Follow these steps to resolve the issue:
-
Install the .NET 9 SDK if it is not already installed. Download it from the official .NET website: Download .NET 9.0.
-
Repair your Visual Studio installation to ensure all necessary runtime components are available:
- Open the Visual Studio Installer.
- Locate your Visual Studio installation.
- Select More > Repair.
- Follow the instructions to complete the repair process. Refer to the Visual Studio repair guide.
-
After completing these steps, try creating a new VB or C# project using the Telerik Visual Studio extension.