Hi!
Are the users able to login to their mailboxes? No issues reported so far?
This error is generated in unity if a subscriber is not able to login into the mailbox.
If everything is working fine in your system you can schedule a system reboot as I've seen this clears the error. Otherwise, you can enable Unity traces to see what's causing the error.
Regards,
Teresa.
Regards,
Tere.
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