In order to resolve this issue you must perform the following steps on your Exchange box.
To create a secondary virtual directory for Exchange that is based on steps 1 through 7 of the following procedure, make sure that forms-based authentication is disabled for the Exchange virtual directory before you make the copy. Before you follow these steps, disable forms-based authentication in Exchange System Manager. Then restart Internet Information Services (IIS). To do this, follow these steps:
You must use Internet IIS Manager to create this virtual directory for Exchange ActiveSync and Outlook Mobile Access to work. If you are using Windows Server 2003, follow these steps:
Note If the server is Microsoft Windows Small Business Server 2003 (SBS), the name of the Exchange OMA virtual directory must be exchange-oma.
The integrated setup of Microsoft Windows Small Business Server 2003 creates the exchange-omavirtual directory in IIS. Additionally, it points the ExchangeVDir registry key to /exchange-omaduring the initial installation. Other SBS wizards, such as the Configure E-mail and Internet Connection Wizard (CEICW) also expect the virtual directory name in IIS to be exchange-oma.