If you run the Exchange 2010 Remote Connectivity Analyzer (ExRCA) and you get the following message it means the Server attribute is set on the EXPR provider incorrectly.
Autodiscover settings for Outlook Anywhere are being validated.
ExRCA wasn't able to validate Outlook Anywhere Autodiscover settings.
The AuthPackage wasn't specified in the EXPR section of the Autodiscover response.
Simply remove the Server attribute and set it to Null.
Set-OutlookProvider EXPR -Server $null
This will resolve your problem.