The name of the security certificate is invalid or does not match the name of the site.
Note This scenario applies only to Outlook clients that connect to Exchange from inside the local network.
This scenario does not apply to remote Outlook clients that connect to Exchange by using Outlook Anywhere.

http://support.microsoft.com/kb/940726/nl (dutch)
https://support.microsoft.com/en-us/kb/940726 (english)

1.Start the Exchange Management Shell.

2.Change the Autodiscover URL in the Service Connection Point.
The Service Connection Point is stored in the Active Directory directory service. To change this URL, type the following command, and then press Enter:
Set-ClientAccessServer -Identity CAS_Server_Name -AutodiscoverServiceInternalUrl https://mail.contoso.com/autodiscover/autodiscover.xml

3.Change the InternalUrl attribute of the EWS. To do this, type the following command, and then press Enter:
Set-WebServicesVirtualDirectory -Identity "CAS_Server_Name\EWS (Default Web Site)" -InternalUrl https://mail.contoso.com/ews/exchange.asmx

4.Change the InternalUrl attribute for Web-based Offline Address Book distribution. To do this, type the following command, and then press Enter:
Set-OABVirtualDirectory -Identity "CAS_Server_name\oab (Default Web Site)" -InternalUrl https://mail.contoso.com/oab

5. Only for Exchange 2007
Change the InternalUrl attribute of the UM Web service. To do this, type the following command, and then press Enter:
Set-UMVirtualDirectory -Identity "CAS_Server_Name\unifiedmessaging (Default Web Site)" -InternalUrl https://mail.contoso.com/unifiedmessaging/service.asmx

6.Open IIS-beheer.
7.Expand the local computer, and then expand Application Pools.
8.Right-click MSExchangeAutodiscoverAppPool, and then click Recycle.