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Exchange Backup Fails With: "Invalid serialized stream, unknown opcode found: 4"

KB ID: 4540
Product: Veeam Backup for Microsoft 365 | 7.0 | 7a
Published: 2024-01-22
Last Modified: 2024-04-16
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As of April 15th, 2024, Veeam Support is observing an increase in the number of customers reporting that they are facing the issue documented in this article. The solution remains the same: ensure that the latest version of Veeam Backup for Microsoft 365 is installed.

The prevailing theory is that Microsoft is rolling out the changes that initially caused this issue to more customers. This rollout is causing customers who were not initially impacted in January to experience the problem now.

This notice will be updated as more information becomes available.

Update 2024-04-16: If the issue persists after upgrading to the latest version, ensure all remote proxies are upgraded, and then retry the jobs.

Challenge

Starting around January 19th, 2024, Exchange backup within Veeam Backup for Microsoft 365 may fail with the following error:

Invalid serialized stream, unknown opcode found: 4

Cause

Veeam has observed that there have been changes to the Serialized Property for Exchange items.
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