You get this error when testing ActiveSync using the Exchange Connectivity Analyzer.

SOLUTION

From the Exchange Shell run:
Get-WebServicesVirtualDirectory | FL InternalURL, ExternalURL
Set-WebServicesVirtualDirectory -Identity -InternalURL – ExternalURL

Get-ActivesyncVirtualDirectory | FL InternalURL, ExternalURL
Set-ActiveSyncVirtualDirectory -Identity “ServerMicrosoft-Server-ActiveSync (Default Web Site)” -ExternalUrl https://servername.domain.com/Microsoft-Server-ActiveSync
The Identity parameter uniquely identifies the Exchange ActiveSync virtual directory to be configured. This value must be websiteMicrosoft-Server-ActiveSync (Default Web Site).
The ExternalUrl parameter specifies the URL used to connect to the virtual directory from outside the network firewall.

Get-AutoDiscoverVirtualDirectory | FL InternalURL, ExternalURL
Set-AutoDiscoverVirtualDirectory -Identity “ServerAutodiscover (Default Web Site)” -InternalURL https://autodiscover.domain.com/AutoDiscover/AutoDiscover.xml
-ExternalUrl https://autodiscover.domain.com/AutoDiscover/AutoDiscover.xml

From: http://marcskb.wikispaces.com/None+of+the+expected+XML+elements+were+found+in+the+XML+response