Troubleshooting HTTP Error Codes (403, 500, 502, 503) Print

Understanding and Resolving HTTP Error Codes

This guide helps diagnose and fix common HTTP errors on Windows/IIS hosting.

403 Forbidden Error

Common Causes:

• Missing default document (index.html, default.aspx, etc.)
• Directory browsing disabled with no default page
• IP restrictions or access rules blocking access
• Incorrect file/folder permissions
• web.config authorization rules

Solutions:

1. Add Default Document:

1. In Plesk, go to Websites & Domains
2. Select Hosting Settings
3. Verify default documents are configured

2. Check web.config Authorization:

<!-- Remove restrictive authorization -->
<authorization>
  <allow users="*"/>
</authorization>

3. Enable Directory Browsing (if needed):

<system.webServer>
  <directoryBrowse enabled="true" />
</system.webServer>

500 Internal Server Error

Common Causes:

• Syntax errors in web.config
• Application code exceptions
• Missing dependencies or assemblies
• Database connection failures
• Insufficient permissions on app folders

Solutions:

1. Enable Detailed Errors (temporarily):

<system.webServer>
  <httpErrors errorMode="Detailed" />
</system.webServer>

<!-- For ASP.NET -->
<system.web>
  <customErrors mode="Off"/>
</system.web>

2. Check Application Logs:

• In Plesk: Websites & Domains > Logs
• Look for entries with status code 500
• Check Windows Event Viewer (if available)

3. Validate web.config:

• XML must be well-formed
• All tags properly closed
• No duplicate sections

502 Bad Gateway Error

Common Causes:

• Application pool crash or timeout
• ASP.NET Core application not starting
• Kestrel server not responding
• Incorrect hosting model configuration

Solutions:

For ASP.NET Core Applications:

1. Check stdout log in the application folder
2. Verify .NET runtime version is installed
3. Ensure web.config has correct hosting settings:

<aspNetCore processPath="dotnet"
            arguments=".\YourApp.dll"
            stdoutLogEnabled="true"
            stdoutLogFile=".\logs\stdout"
            hostingModel="InProcess">
</aspNetCore>

503 Service Unavailable

Common Causes:

• Application pool stopped or crashed
• Server overloaded or under maintenance
• Resource limits exceeded

Solutions:

1. Contact support to restart your application pool
2. Check if you're exceeding hosting plan limits
3. Review recent code changes that may cause crashes

Quick Diagnostic Steps

Important: Remember to disable detailed error messages in production after debugging!