---
title: "Why does my .NET app fail to start after changing the runtime version?"  
description: "Why does my .NET app fail to start after changing the runtime version?"  
author: "John Smith"  
published: 2026-09-21  
canonical: https://answers.mindstick.com/qa/117258/why-does-my-net-app-fail-to-start-after-changing-the-runtime-version  
category: "troubleshooting"  
tags: ["troubleshooting", "iis", "runtime"]  
reading_time: 1 minute  

---

# Why does my .NET app fail to start after changing the runtime version?

## Runtime Mismatch

You upgraded the .NET runtime on your server, but the application pool still points to the older version. The result? A crash on launch with a cryptic "Unable to find the specified file" error.

### Checking the actual runtime

Open a command prompt and run `dotnet --list-runtimes`. If the version you need is missing, install it via the Microsoft Install Script or your OS package manager. Do not assume the global SDK installation covers the server runtime.

- Verify the app pool in IIS points to the correct .NET CLR version.
- Restart the application pool after any runtime change.
- Check the event viewer for binding failures before reinstalling anything.


---

Original Source: https://answers.mindstick.com/qa/117258/why-does-my-net-app-fail-to-start-after-changing-the-runtime-version

Copyright © MindStick Software Pvt. Ltd. This Markdown version is provided for developers, AI systems, and offline reading.