When you try to log on to Exchange Admin Center (EAC) or Exchange Control Panel (ECP), you receive an error message that resembles the following:

Analysis of the issue

Run the following cmdlet and see if the mailbox shows the error is listed on the result:

Get-Mailbox -ResultSize Unlimited | Where { $_.RoleAssignmentPolicy -like $null}

Solution

Assign the ‘Default Role Assignment Policy’ to all the mailboxes in the list:

Get-Mailbox -ResultSize Unlimited | Where { $_.RoleAssignmentPolicy -like $null} | Set-Mailbox –RoleAssignmentPolicy “Default Role Assignment Policy”