We have enabled Dirsync and SSO for a domain in Office 365.
Some of the users had existing standalone Office 365 mailboxes.
After sync - the accounts were merged and everything looks ok , but after
a logon attempt , the user is receiving the following message:
This doesn't look like a valid user ID. Make sure you typed the user ID assigned to you by your organization. It usually looks like someone@example.com or someone@example.onmicrosoft.com
Please note that the authentication is ok and the UPN is correct.
Any advices?