Question 1

Why does my app work in Visual Studio but fail on IIS?

Accepted Answer

Visual Studio runs your app directly with the dotnet CLI, using whatever runtime is installed on your dev machine. IIS uses ANCM, which has different requirements. The most common cause of this gap: you have .NET installed on your dev machine, but haven't installed the hosting bundle on the server.

Question 2

Do I need the SDK or the hosting bundle on the server?

Accepted Answer

The hosting bundle. The SDK is for development. The server just needs the runtime and ANCM, which the hosting bundle installs. Installing the SDK on a production server works but includes unnecessary tools.

Question 3

Can I have multiple .NET versions installed at once?

Accepted Answer

Yes, .NET is designed for side-by-side installations. You can have .NET 6, 7, and 8 all installed at the same time. IIS will use the version your app specifies.

Question 4

My web.config looks correct, but I still get 500.31. What now?

Accepted Answer

Enable stdout logging, reproduce the error, and read the log. The actual error is almost always in the log. The browser error page is deliberately unhelpful for security reasons.

Question 5

Does this error affect Azure App Service?

Accepted Answer

On Azure App Service, the runtime management is mostly handled for you. You're more likely to see a different error (like ANCM in-process startup failure) if your app crashes on startup. But 500.31 can appear on Azure if you've specified a runtime version in your app settings that isn't available in the chosen App Service plan tier.

Question 6

How do I check which version of ANCM is installed?

Accepted Answer

Open IIS Manager. Click the server. Double-click Modules. Find AspNetCoreModuleV2. Right-click it and choose Properties. The DLL path shown there tells you the version. You can also check the file version of the DLL directly in File Explorer.

Question 7

Is 500.31 a security risk?

Accepted Answer

The error itself isn't. The browser page shows minimal detail. The risk comes from leaving stdout logging enabled in production, which can expose startup exceptions, including connection strings, if your app logs them. Always disable stdout logging after debugging.

Development

Solved: Fix HTTP Error 500.31 ASP.NET Core Runtime (2026)

Error: Gradle Task AssembleDebug Failed With Exit Code 1

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