Office 365 Exchange Public Folder Permission Error: "Exception has been thrown by the target of an invocation."

I'm trying to create a new Office 365 Exchange Public Folder. No other Public Folders exist. 
From Office 365 Exchange Admin Center, I create Public Folder using the following process:

1. Create Public folders Mailbox. Save completes successfully
2. Create Public Folder. Save completes successfully
3. Under Public Folder permissions, select Manage
4. Add Users to Public Folder. From Browse, I select user. (Recipient Type is “User Mailbox”). Change Permission level to Owner. Save User completes successfully
5. However, when I try to Save, I receive the following Error: “Exception has been thrown by the target of an invocation.”

I have given the Public folders over 24 hours to update. I have deleted and recreated Public folder mailbox and Public folder with same result.
Please let me know if you need additional information. Any suggestions would be much appreciated.
Thank you! Chip