Event Hubs messaging exceptions - .NET (legacy)

This section lists the .NET exceptions generated by .NET Framework APIs.


Some of the exceptions listed in the article apply only to legacy Event Hubs .NET library. For example: Microsoft.ServiceBus.* exceptions.

For information about the EventHubsException raised by the new .NET library, see EventHubsException - .NET

Exception categories

The Event Hubs .NET APIs generate exceptions that can fall into the following categories, along with the associated action you can take to try to fix them:

Exception types

The following table lists messaging exception types, and their causes, and notes suggested action you can take.

Exception Type Description/Cause/Examples Suggested Action Note on automatic/immediate retry
TimeoutException The server didn't respond to the requested operation within the specified time, which is controlled by OperationTimeout. The server may have completed the requested operation. This exception can happen because of network or other infrastructure delays. Check the system state for consistency and retry if necessary.
See TimeoutException.
Retry might help in some cases; add retry logic to code.
InvalidOperationException The requested user operation isn't allowed within the server or service. See the exception message for details. For example, Complete generates this exception if the message was received in ReceiveAndDelete mode. Check the code and the documentation. Make sure the requested operation is valid. Retry won't help.
OperationCanceledException An attempt is made to invoke an operation on an object that has already been closed, aborted, or disposed. In rare cases, the ambient transaction is already disposed. Check the code and make sure it doesn't invoke operations on a disposed object. Retry won't help.
UnauthorizedAccessException The TokenProvider object couldn't acquire a token, the token is invalid, or the token doesn't contain the claims required to do the operation. Make sure the token provider is created with the correct values. Check the configuration of the Access Control Service. Retry might help in some cases; add retry logic to code.
One or more arguments supplied to the method are invalid. The URI supplied to NamespaceManager or Create contains path segment(s). The URI scheme supplied to NamespaceManager or Create is invalid. The property value is larger than 32 KB. Check the calling code and make sure the arguments are correct. Retry will not help.
Microsoft.ServiceBus.Messaging MessagingEntityNotFoundException

Microsoft.Azure.EventHubs MessagingEntityNotFoundException
Entity associated with the operation does not exist or it has been deleted. Make sure the entity exists. Retry will not help.
MessagingCommunicationException Client is not able to establish a connection to Event Hub. Make sure the supplied host name is correct and the host is reachable. Retry might help if there are intermittent connectivity issues.
Microsoft.ServiceBus.Messaging ServerBusyException

Microsoft.Azure.EventHubs ServerBusyException
Service is not able to process the request at this time. Client can wait for a period of time, then retry the operation.
See ServerBusyException.
Client may retry after certain interval. If a retry results in a different exception, check retry behavior of that exception.
MessagingException Generic messaging exception that may be thrown in the following cases: An attempt is made to create a QueueClient using a name or path that belongs to a different entity type (for example, a topic). An attempt is made to send a message larger than 1 MB. The server or service encountered an error during processing of the request. See the exception message for details. This exception is usually a transient exception. Check the code and ensure that only serializable objects are used for the message body (or use a custom serializer). Check the documentation for the supported value types of the properties and only use supported types. Check the IsTransient property. If it is true, you can retry the operation. Retry behavior is undefined and might not help.
MessagingEntityAlreadyExistsException Attempt to create an entity with a name that is already used by another entity in that service namespace. Delete the existing entity or choose a different name for the entity to be created. Retry will not help.
QuotaExceededException The messaging entity has reached its maximum allowable size. This exception can happen if the maximum number of receivers (which is 5) has already been opened on a per-consumer group level. Create space in the entity by receiving messages from the entity or its subqueues.
See QuotaExceededException
Retry might help if messages have been removed in the meantime.
MessagingEntityDisabledException Request for a runtime operation on a disabled entity. Activate the entity. Retry might help if the entity has been activated in the interim.
Microsoft.ServiceBus.Messaging MessageSizeExceededException

Microsoft.Azure.EventHubs MessageSizeExceededException
A message payload exceeds the 1-MB limit. This 1-MB limit is for the total message, which can include system properties and any .NET overhead. Reduce the size of the message payload, then retry the operation. Retry will not help.


QuotaExceededException indicates that a quota for a specific entity has been exceeded.

This exception can happen if the maximum number of receivers (5) has already been opened on a per-consumer group level.

Event Hubs

Event Hubs has a limit of 20 consumer groups per Event Hub. When you attempt to create more, you receive a QuotaExceededException.


A TimeoutException indicates that a user-initiated operation is taking longer than the operation timeout.

For Event Hubs, the timeout is specified either as part of the connection string, or through ServiceBusConnectionStringBuilder. The error message itself might vary, but it always contains the timeout value specified for the current operation.

Timeouts are expected to happen during or in-between maintenance operations such as Event Hubs service updates (or) OS updates on resources that run the service. During OS updates, entities are moved around and nodes are updated or rebooted, which can cause timeouts. For service level agreement (SLA) details for the Azure Event Hubs service, see SLA for Event Hubs.

Common causes

There are two common causes for this error: incorrect configuration, or a transient service error.

  • Incorrect configuration The operation timeout might be too small for the operational condition. The default value for the operation timeout in the client SDK is 60 seconds. Check to see if your code has the value set to something too small. The condition of the network and CPU usage can affect the time it takes for a particular operation to complete, so the operation timeout should not be set to a small value.
  • Transient service error Sometimes the Event Hubs service can experience delays in processing requests; for example, during periods of high traffic. In such cases, you can retry your operation after a delay, until the operation is successful. If the same operation still fails after multiple attempts, visit the Azure service status site to see if there are any known service outages.


A Microsoft.ServiceBus.Messaging.ServerBusyException or Microsoft.Azure.EventHubs.ServerBusyException indicates that a server is overloaded. There are two relevant error codes for this exception.

Error code 50002

This error can occur for one of two reasons:

  • The load isn't evenly distributed across all partitions on the event hub, and one partition hits the local throughput unit limitation.

    Resolution: Revising the partition distribution strategy or trying EventHubClient.Send(eventDataWithOutPartitionKey) might help.

  • The Event Hubs namespace doesn't have sufficient throughput units (you can check the Metrics screen in the Event Hubs namespace window in the Azure portal to confirm). The portal shows aggregated (1 minute) information, but we measure the throughput in real time – so it's only an estimate.

    Resolution: Increasing the throughput units on the namespace can help.

    You can configure throughput units on the Scale page or Overview page of your Event Hubs namespace page in the Azure portal. Or, you can use Auto-inflate, which automatically scales up by increasing the number of throughput units, to meet usage needs.

    Throughput units (TUs) apply to all event hubs in an Event Hubs namespace. It means that you purchase TUs at the namespace level and are shared among the event hubs under that namespace. Each TU entitles the namespace to the following capabilities:

    • Up to 1 MB per second of ingress events (events sent into an event hub), but no more than 1000 ingress events, management operations, or control API calls per second.
    • Up to 2 MB per second of egress events (events consumed from an event hub), but no more than 4096 egress events.
    • Up to 84 GB of event storage (enough for the default 24-hour retention period).

    On the Overview page, in the Show metrics section, switch to the Throughput tab. Select the chart to open it in a larger window with 1-minute intervals on the x-axis. Look at the peak values and divide them by 60 to get incoming bytes/second or outgoing bytes/second. Use similar approach to calculate number of requests per second at peak times on the Requests tab.

    If you see values higher than number of TUs * limits (1 MB per second for ingress or 1000 requests for ingress/second, 2 MB per second for egress), increase the number of TUs by using the Scale (on the left menu) page of an Event Hubs namespace to manually scale higher or to use the Auto-inflate feature of Event Hubs. Note that auto-Inflate can only increase up to 20 TUS. To raise it to exactly 40 TUs, submit a support request.

Error code 50008

This error should rarely occur. It happens when the container running code for your namespace is low on CPU – not more than a few seconds before the Event Hubs load balancer begins.

Resolution: Limit calls to the GetRuntimeInformation method. Azure Event Hubs supports up to 50 calls per second per consumer group to the GetRuntimeInfo per second. You may receive an exception similar to the following one once the limit is reached:

ExceptionId: 00000000000-00000-0000-a48a-9c908fbe84f6-ServerBusyException: The request was terminated because the namespace 75248:aaa-default-eventhub-ns-prodb2b is being throttled. Error code : 50008. Please wait 10 seconds and try again.

Next steps

You can learn more about Event Hubs by visiting the following links: