Client authentication methods for ActiveSync are configured on this server {0}. You can modify this setting via PowerShell. ...

Client authentication methods for ActiveSync are configured on this server {0}. You can modify this setting via PowerShell.  Example: 'set-ActiveSyncVirtualDirectory -Identity "{1}" -BasicAuthEnabled $true' or 'set-ActiveSyncVirtualDirectory -Identity "{1}" -ClientCertAuth Accepted' or both to enable authentication support.