Unable to load DLL 'mqrt.dll'

Question

I've developed a WCF Service which is hosted as a Windows Service and exposes a MSMQ endpoint.

I have the client app on SERVER1, and the MSMQ and WCF Service on SERVER2.

When the SERVER1/ClientApp attempts to push a message on to the SERVER2 MSMQ, I get the following errror:

    System.TypeInitializationException: The type initializer for 'System.ServiceModel.Channels.Msmq' threw an exception. ---> System.DllNotFoundException: Unable to load DLL 'mqrt.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)
       at System.ServiceModel.Channels.UnsafeNativeMethods.MQGetPrivateComputerInformation(String computerName, IntPtr properties)
       at System.ServiceModel.Channels.MsmqQueue.GetMsmqInformation(Version& version, Boolean& activeDirectoryEnabled)
       at System.ServiceModel.Channels.Msmq..cctor()
       --- End of inner exception stack trace ---
       at System.ServiceModel.Channels.Msmq.EnterXPSendLock(Boolean& lockHeld, ProtectionLevel protectionLevel)
       at System.ServiceModel.Channels.MsmqOutputChannel.OnSend(Message message, TimeSpan timeout)
       at System.ServiceModel.Channels.OutputChannel.Send(Message message, TimeSpan timeout)
       at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)
       at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation)
       at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)

Exception rethrown at [7]: 
   at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
   at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
   at FacilityManager.Service.NotificationsProcessorServiceReference.INotificationsProcessor.SendNewReactiveTaskNotifications(NewReactiveTaskDataContract newReactiveTaskDataContract)

Both SERVER1 and SERVER2 are running Windows Server 2008 R2 Enterprise (6.1 SP1), and both have had MSMQ installed via the Add Features in Server Manager.

I understand that the DLL is missing (fairly obvious from the error!), but I've no idea what I should be installing to get the dll where it should be.

A search in Windows Explorer shows that the DLL is present in the following directories on both servers....

• C:\Windows\System32
• C:\Windows\SysWOW64
• C:\Windows\winsxs\x86_microsoft-windows-msmq-runtime-core_31bf3856ad364e35_6.1.7601.17514_none_5768e2ad17453bd6
• C:\Windows\winsxs\amd64_microsoft-windows-msmq-runtime-core_31bf3856ad364e35_6.1.7601.17514_none_b3877e30cfa2ad0c

Any help appreciated.

Answer 1

An obvious aside; If you don't have the Windows Feature -> Microsoft Message Queue (MSMQ) Server installed then you will get this error. Simply go to Programs and Features and then Turn Windows Feature on or off.

Answer 2

This can be caused by your service on SERVER2 starting up and finishing its initialization before MSMQ is done initializing itself. The easiest way to test this is to restart the service hosting the WCF MSMQ endpoint. If the WCF service is hosted in IIS, perhaps bouncing the app pool will do the same thing, but I do not know for sure -- I've never dealt with an IIS hosted MSMQ endpoint.

If restarting the service fixes your problem and your own service is a Windows service, you can then add MSMQ as a dependency to your own service so that it will delay its startup until MSMQ is ready. This answer on Server Fault describes how to do it. Incidentally, the service you want to depend on is called "Message Queueing"

Answer 3

I'm none the wiser but things are working now.

After hours on SO and Google, I ended up just checking that MSMQ was installed on both Servers by writing a quick console application with the code grabbed from here...

https://stackoverflow.com/a/16104212/192999

I ran the console app on both Server1 and Server2 and both came back with a result of True to IsMsmqInstalled.

I then ran my application and the "Unable to load DLL 'mqrt.dll'" error was no longer being raised.

I don't know if the call to NativeMethods.LoadLibrary("Mqrt.dll"); registered the DLL or something, but it certainly fixed my problem.

I hope this helps someone in the future!