Troubleshooting HTTP 500 Startup Errors (ASP.NET Core)

If your ASP.NET Core application returns a generic "This page isn’t working (HTTP ERROR 500)" message immediately upon visiting it, the application is likely crashing during its startup sequence.

Common causes include:

• Database connection failures (e.g., incorrect connection string in appsettings.json).
• Missing dependencies or unhandled exceptions in Program.cs or Startup.cs.
• Failures during Entity Framework migrations.
• Missing configuration values (e.g., Social Login secrets).

Since the app crashes before it can load, it cannot display a friendly error page. Use the methods below to find the actual error message.

Method 1: Automated Startup Diagnostics (Recommended)

We provide a built-in tool that forces your application to restart and immediately captures any errors logged to the Windows Event Log during the crash.

1. Navigate to the Event Viewer
   • Log in to the control panel.
   • Navigate to Websites and click on your website name.
   • Select the Event viewer tab.
2. Run the Test
   • Click the RUN STARTUP DIAGNOSTICS link (located near the top right).
   • A dialog will appear explaining the process (Recycling the app pool, calling the default URL, and retrieving logs).
   • Click RUN THE TEST.
3. View Results
   • A new browser tab will open.
   • If your application crashed, this page will display the specific stack trace or exception message from the Windows Event Log.
   • If the page says "The application returned OK code," your application successfully started, and the issue may be related to internal routing or permissions rather than a startup crash.

Method 2: Enable Stdout Logging (Manual)

If the diagnostics tool does not reveal the issue, you can enable internal ASP.NET Core logging to capture raw output to a file.

1. Edit Web.Config
   • Go to the File manager tab for your website.
   • Edit the web.config file.
   • Find the <aspNetCore> element.
   • Change stdoutLogEnabled="false" to stdoutLogEnabled="true".
   • Ensure the path is set correctly, e.g., stdoutLogFile=".\logs\stdout".
2. Create the Logs Folder
   • Crucial: You must ensure the logs folder exists in your root directory. If it is missing, create it using the File manager or FTP.
3. Reproduce the Error
   • Visit your website again to trigger the error.
   • Check the /logs/ folder. You should see a new text file containing the detailed startup error.