Hi @DieterPa,
To troubleshoot the error message "[1200]" while adding the second OneDrive for Business account, you can follow these steps:
1. Clear Credentials: Access the Credential Manager on your Windows laptop. Look for any cached credentials associated with the second OneDrive for Business account and delete them. After that, try to add the account again.
Accessing Credential Manager - Microsoft Support
2. Reconfigure Account: Navigate to the OneDrive settings on your laptop, sign out of the second OneDrive for Business account, and restart your computer. Sign in again with the second account to reconfigure it.
How to access OneDrive settings - Microsoft Support
3. Check Firewall and Antivirus: Disable any antivirus or firewall programs temporarily, as they may be interfering with the authentication process. Try adding the second OneDrive for Business account while these security programs are disabled.
4. Repair OneDrive: Access the Control Panel on your laptop and locate "Programs" or "Programs and Features." Find OneDrive in the list, right-click on it, and choose "Repair" or "Change." Follow the instructions to complete the repair process. Afterward, restart your computer and attempt to add the second account again.
5. Reset OneDrive: Resetting Microsoft OneDrive can sometimes resolve sync issues and resets all OneDrive settings. OneDrive will perform a full sync after the reset.
Reset OneDrive - Microsoft Support
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Kindest regards
Leon Pavesic