Type Not Registered in the Serializer

If this exception is encountered when using NServiceBus in an ASP.NET application after upgrading the code of the app, it is usually due to files that are locked.

Exception details

Server Error in '/' Application. Type XYZ was not registered in the serializer. Check that it appears in the list of configured assemblies/types to scan. Description: An unhandled exception occurred during the execution of the current web request. Review the stack trace for more information about the error and where it originated in the code.


  1. Stop the w3svc process of the website being upgraded.
  2. Delete temporary ASP.NET files, usually found in the directory c:\Windows\Microsoft.NET\Framework(64)\{version}\.
  3. Run the application again. The exception should no longer happen.

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