503 Service Unavailable Error "The Module DLL Failed To Load. The Data Is The Error"

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503 Service Unavailable error (The Module DLL failed to load. The data is the error)

Symptom: When browsing any site hosted on IIS and HTTP Error 503 Service Unavailable error is thrown.

Root Cause: Some required IIS components are NOT loading properly. e.g. (The Module DLL failed to load. The data is the error.). This can happen when that feature is not installed properly on the server.

Sample errors for reference.

  • The Module DLL C:\WINDOWS\System32\inetsrv\webdav.dll failed to load. The data is the error.

Resolution:

  1. First check if the Application Pool for server is started, and if stopped restart it
  2. If the Application Pool is started and stopped again then review the Windows Application Event logs for errors with source “IIS-W3SVC-WP”
  3. The Module DLL failed to load. The data is the error. Please find below screen shot for reference.

  1. Check if system is referring failed to load DLL in "C:\Windows\System32\inetsrv\config\applicationHost.config" file. If yes, identify the associated Role/Service and install it on server. In this case "WebDAV Publishing" IIS Module. Find below screen shot for reference.