Setup Exchange ActiveSync and Outlook Mobile Access

I'm attempting to setup email synchronization support for users with smart phones.  I'm running Exchange 2003 (with current patches).  The first user device I was trying was a Verizon XV6700.  It can sync to the user's desktop successfully, but is not synching to Exchange.

The user is setup in AD for all Mobile Services.  

Looking at IIS on the Exchange server, the OMA website appears to be set correctly.  Outlook Web Access is working, so I know I've got a good connection to the server.  However, when I attempt to connect to the OMA website, I get prompted for my username/password, then get the error,
"  A System error has occurred while processing your request. Please try again. If the problem persists, contact your administrator."

On the Exchange server's Event Log for Applications, I get a 1503 Event ID, with the source "MSExchangeOMA."  Here's the text of the error:
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An unknown error occurred while processing the current request:
Message: The remote server returned an error: (403) Forbidden.
Source: Microsoft.Exchange.OMA.ExchangeDataProvider
Stack trace:
   at Microsoft.Exchange.OMA.ExchangeDataProvider.OmaWebRequest.GetRequestStream()
   at Microsoft.Exchange.OMA.ExchangeDataProvider.ExchangeServices.GetSpecialFolders()
   at Microsoft.Exchange.OMA.ExchangeDataProvider.ExchangeServices..ctor(UserInfo user)

Message: Exception has been thrown by the target of an invocation.
Source: mscorlib
Stack trace:
   at System.Reflection.RuntimeConstructorInfo.InternalInvoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean isBinderDefault)
   at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
   at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
   at Microsoft.Exchange.OMA.UserInterface.Global.Session_Start(Object sender, EventArgs e)

Message: Exception of type Microsoft.Exchange.OMA.DataProviderInterface.ProviderException was thrown.
EventMessage:
UserMessage: A System error has occurred while processing your request. Please try again. If the problem persists, contact your administrator.
Source: Microsoft.Exchange.OMA.UserInterface
Stack trace:
   at Microsoft.Exchange.OMA.UserInterface.Global.Session_Start(Object sender, EventArgs e)
   at System.Web.SessionState.SessionStateModule.RaiseOnStart(EventArgs e)
   at System.Web.SessionState.SessionStateModule.CompleteAcquireState()
   at System.Web.SessionState.SessionStateModule.BeginAcquireState(Object source, EventArgs e, AsyncCallback cb, Object extraData)
   at System.Web.AsyncEventExecutionStep.System.Web.HttpApplication+IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)


For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.
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What's the next step to resolve this?