MS 365 Backups are failing with "Exception occurred - Reason: Object reference not set to an instance of an object." (4378982)

Backup fails with the following errors:

03/31/2025 22:00:03 : Exception occurred - Reason: Object reference not set to an instance of an object.
03/31/2025 22:00:03 : Reason: Code: generalException
Message: An error occurred sending the request.

When checking the Plug-in for MS 365 the user list for certain apps, for example, OneDrive, will not open. 

These errors suggest the plugin is trying to access something (like a user object or OneDrive resource) that either no longer exists, isn’t accessible, or has a broken reference. This is usually caused by expired or misconfigured Tenant Credentials or missing permissions in Azure AD. 

Step-by-Step to Update Tenant Credentials:

1. Go to Configuration > Manage Clients

   • Locate and select the NetVault client where the M365 plug-in is installed (e.g., NVSRV1)

2. Right-click the Plug-in for Microsoft 365 node or use the gear icon/menu

   • Choose Configure

3. In the Add Tenant / Edit Tenant screen:

   • Choose Tenant Credentials (since the original config likely used App ID and Secret)

4. Enter the following values:

   • Application Domain:
     Typically your verified Microsoft 365 domain (e.g., n28s.onmicrosoft.com)

   • Application ID:
     Found under Azure Active Directory > App registrations > Your App > Overview

   • Application Password:
     This is your client secret. If expired, generate a new one under: Azure AD > App registrations > Your App > Certificates & secrets > New client secret

   • 

5. (Optional) Enable Teams Backup:

   • Check Enter Global Administrator Credentials

     • Use UPN format: adminuser@n28s.onmicrosoft.com

     • This account must be:

       • A Global Administrator

       • A member/owner of Teams

6. Click OK to save the updated configuration

7. Return to Manage Sets > Plug-in for Microsoft 365 > OneDrive > Users

   • The user list should now populate correctly if credentials are valid and permissions are intact.