If you are using Windows Mobile you will need to add the correct root certificate for our SSL issuer before ActiveSync will start working.

If you get an error like this "invalid server security certificate" and your device is running Windows Mobile then following the guidance in the Microsoft link below should resolve this.

http://support.microsoft.com/kb/915840

If you do decide to follow these instructions then you will need the root certificate for GeoTrust's Quick SSL certificates which can be downloaded from here:

http://www.geotrust.com/resources/root-certificates/

The correct Geotrust root certificate should be "Equifax Secure Global eBusiness CA-1 (DER encoded X.509)".