SmartPhone needs client certificate – ActiveSync error 85030037

If you have a SmartPhone that won’t sync with your Exchange 2003 SP2, mentioning error 85030037, you may want to try the following:
Open IIS Management on your Exchange 2003 server.
Right click Microsoft Server ActiveSync and select Properties.
Select the tab Directory Security and click Edit.
Confirm that your current setting is “Accept client certificates” and change it to “Ignore client certificates”.
Restart IIS and be sure to reset your server settings on your SmartPhone. You can do this by changing the server name to something invalid (peel off the first or last character), save the settings on your SmartPhone, let it synchronize (this will obviously fail) and change the server name back to the right server name. Reboot your SmartPhone and voilà!