Getting Started

NServiceBus host troubleshooting

Component: NServiceBus Host

Host fails to start due to System.Reflection.ReflectionTypeLoadException

The host does not start and the console or log contains the following exception message:

System.Reflection.ReflectionTypeLoadException Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.


Fatal,NServiceBus.Hosting.Windows.WindowsHost,Start failure,"System.Reflection.ReflectionTypeLoadException Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information. at System.Reflection.RuntimeModule.GetTypes(RuntimeModule module)
at System.Reflection.Assembly.GetTypes()
at System.Linq.Enumerable.<SelectManyIterator>d__17`2.MoveNext()
at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at NServiceBus.Hosting.Profiles.ProfileManager.ActivateProfileHandlers(EndpointConfiguration config) in C:\BuildAgent\work\3fdd02ec65f005b\src\NServiceBus.Hosting.Windows\Profiles\ProfileManager.cs:line 104
at NServiceBus.GenericHost.PerformConfiguration(Action`1 moreConfiguration) in C:\BuildAgent\work\3fdd02ec65f005b\src\NServiceBus.Hosting.Windows\GenericHost.cs:line 82
at NServiceBus.GenericHost.<Start>d__1.MoveNext() in C:\BuildAgent\work\3fdd02ec65f005b\src\NServiceBus.Hosting.Windows\GenericHost.cs:line 53
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at NServiceBus.Hosting.Windows.WindowsHost.Start() in C:\BuildAgent\work\3fdd02ec65f005b\src\NServiceBus.Hosting.Windows\WindowsHost.cs:line 32

Verify that:

  1. Assembly binding redirects in the NServiceBus.Host.exe.config are correct and match with any entries generated in the App.config file.
  2. All files in the deployment (sub)folder are correct and no old files are present from previous deployments.

Windows service fails to start due to reaching the timeout period

When a Windows service fails to transition into the SERVICE_RUNNING state before timeout (i.e. fails to complete the start sequence), the following exception messages may be seen in the Windows Event Viewer:

A timeout was reached (30000 milliseconds) while waiting for the XYZ service to connect.
The XYZ service failed to start due to the following error:
The service did not respond to the start or control request in a timely fashion

This often occurs when a dependency is not available in time during the start process. Another symptom is that the service will start at a later time without issue.

This problem can be mitigated by:

  • If the service is started automatically, configuring the service to start with delayed-auto set, such that the service will not start until all other "automatic" services are started
  • Configuring service dependencies to ensure they are started before the service starts
  • Enabling service recoverability to ensure the service will automatically restart in case start fails