By default, IIS and ASP.NET hide detailed error information to prevent revealing sensitive information about your web application:

Sometimes you need to see error details (think shared hosting). Add these entries to your web.config file to disable generic errors:

<configuration>
  <system.web>
    <customErrors mode="Off" />
  </system.web>

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

Resources

• How to Use HTTP Detailed Errors in IIS 7.0
• What to expect from IIS7 custom error module
• IIS 7 Error Pages taking over 500 Errors
• IIS7 Overrides customErrors when setting Response.StatusCode?