Check that WMI/Remote Powershell/Remote registry are enabled on the Exchange server.
Check that ports TCP 80/443 are open on the Exchange server (as well as on any firewalls between the OC Scanner and the Exchange server) so that the OC Scanner can connect to Exchange on those ports.
Ensure that the user account running the scan is a part of one of the following security groups:
Exchange View-only Organization Management
Exchange Organization Management
The given issue can also be encountered if we try to scan Windows servers which do not house a full Exchange install, or are not housing any Exchange mailbox/CAS roles. If you encounter a Windows server with only the Exchange Management Tools installed, or an Exchange Edge server, then such servers need to be excluded from the Exchange user scan, by navigating to the OC Configurator > Specific scan file > Servers > Specific entry > User settings > Exchange > Click on the Add button, and add the FQDN/IP of the given server, and toggle the Exchange user scan for this entry to off. Save the changes, run the scan again, and the given error will disappear.
If the OC Scanner server, and the Exchange server, are not in the same AD Domain, then we also need to enable Basic authentication on the Exchange Powershell website, in addition to the above requirements, so we can access the Exchange server, outside of its own AD Domain:
Run Exchange Management Shell (as an Administrator) on the Exchange machine to which you want to connect.
Execute the cmdlet:
Set-PowerShellVirtualDirectory -Identity "PowerShell (Default Web Site)" -BasicAuthentication $true