Microsoft Teams backup fails with the error: Error: Cannot parse page operation response

Backup of Microsoft Teams in Veeam Backup for Microsoft Office 365 fails with the following error: Error: Cannot parse page operation response.

Based on the information provided, this issue aligns with a recent problem that originates from changes made by Microsoft to the GUID format of certain Microsoft Teams components. These changes affect the logic that Veeam Backup for Microsoft Office 365 uses to process Microsoft Teams tabs. 

Veeam provides a hotfix helping to fix this issue. This hotfix is available for Veeam Backup for Microsoft Office 365 5b (builds 5.0.1.225 and 5.0.1.252).

Before installing the hotfix, do the following:

1. Check which version of Veeam Backup for Microsoft Office 365 is installed on your machine. To do this, in the main menu, click Help & Support > About.
2. If you have either 5.0.1.225 or 5.0.1.252 build installed, install the hotfix. If you have another build of Veeam Backup for Microsoft Office 365 5b, update the application and then install the hotfix. For more information on how to apply the cumulative patch, see this Veeam KB article.
3. Stop all backup jobs and restore sessions (if any).
4. Stop Veeam Backup for Microsoft Office 365 Service, Veeam Backup Proxy for Microsoft Office 365 Service, and Veeam Backup for Microsoft Office 365 RESTful API Service.

 To install the hotfix, do the following:

1. In the More Info section below, click the Download button to download the ZIP file.
2. Extract the contents of the ZIP file to the C:\Temp folder. Consider the following:

• If you have Veeam Backup for Microsoft Office 365 build 5.0.1.225 installed, the hotfix files are located in the 320592_Cannot parse page operation response_5.0.1.225 folder. 
• If you have Veeam Backup for Microsoft Office 365 build 5.0.1.252 installed, the hotfix files are located in the 320592_Cannot parse page operation response_5.0.1.252 folder.

1. Run the following cmdlet in Windows PowerShell using the Administrator mode to remove security locks:

Get-ChildItem -Path "C:\Temp\<hotfix files folder>\Veeam.Graph.Teams.dll" -Recurse -Force | Unblock-File

1. In the C:\Program Files\Veeam\Backup365, C:\Program Files\Veeam\Backup365\Packages\Proxy and C:\Program Files\Veeam\Backup and Replication\Explorers\Teams folders, rename or move to another folder the original .dll files and then place the matching .dll files from the hotfix files folder instead of original ones.

After installing the hotfix, do the following:

1. Start Veeam Backup for Microsoft Office 365 Service, Veeam Backup Proxy for Microsoft Office 365 Service, and Veeam Backup for Microsoft Office 365 RESTful API Service.
2. Upgrade the backup proxy servers using the Veeam Backup for Microsoft Office 365 console. For more information, see this section of the Veeam Backup for Microsoft Office 365 User Guide.
3. Back up Microsoft Teams data and check whether the issue still persists. If so, report a problem to Veeam Customer Support and collect log files.