Editing a connection setting in the Active Roles Synchronization Service or running a synchronization with Office 365 results in the following error message:
Processing data from remote server ps.outlook.com failed with the following error message:
Fail to create a runspace because you have exceeded the maximum number of connections allowed : 3 for the policy party : MaxConcurrency. Please close existing runspace and try again.
Microsoft has a Global Throttling Policy which limits simultaneous connections from one client. Only three simultaneous connections are allowed.
Most likely, there are other sessions open in PowerShell from the machine hosting the Active Roles Synchronization Service. Since the Synchronization Service uses PowerShell to communicate with Office 365, other PowerShell sessions can interfere with normal connectivity.
Close all open PowerShell sessions with Office 365.
This could be done using this cmdlet:
Get-PSSession | Remove-PSSession