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.
Solution
The issue was fixed starting with builds 7.0.0.4901 (P20240123) and 7.1.0.1501 (P20240123).
Customers are advised to upgrade to the latest version of Veeam Backup for Microsoft 365, ensure all remote proxies are upgraded, and then retry the jobs.
