如何从sde数据库获得一个featurelayer?

<P>我做一个GIS 服务(只要返回一个featurelayer即可)，可是在vb.net中写了如下代码，总是提示错误：无法找到实现类ESRI.ArcGIS.Carto.FeatureLayer。我已经添加了对ESRI.ArcGIS.Carto的引用，并且在程序的开头已经Imports ESRI.ArcGIS.Carto。不知何原因,请大家指点一下</P>
<P>Imports System.Web.Services<BR>Imports ESRI.ArcGIS.Carto<BR>Imports ESRI.ArcGIS.DataSourcesGDB<BR>Imports ESRI.ArcGIS.esriSystem<BR>Imports ESRI.ArcGIS.Framework<BR>Imports ESRI.ArcGIS.Geodatabase</P>
<P>System.Web.Services.WebService(Namespace := "<a href="http://tempuri.org/AOTestWebService/Service1" target="_blank" >http://tempuri.org/AOTestWebService/Service1</A>")> _<BR>Public Class Service1<BR>    Inherits System.Web.Services.WebService</P>
<P> <WebMethod()> Public Function GetFeatureLay() As IFeatureLayer      'return a featurelayer from sde database<BR>        Dim pWorkspaceFact As IWorkspaceFactory = New SdeWorkspaceFactory<BR>        Dim pWorkspace As IWorkspace<BR>        Dim pFeatureWorkspace As IFeatureWorkspace<BR>        Dim pPropertySet As IPropertySet = New PropertySet<BR>        With pPropertySet<BR>            .SetProperty("SERVER", "xxzx-zy")<BR>            .SetProperty("INSTANCE", "esri_sde")<BR>            .SetProperty("DATABASE", "sde")<BR>            .SetProperty("USER", "sde")<BR>            .SetProperty("PASSWORD", "sde")<BR>            .SetProperty("VERSION", "sde.default")<BR>        End With<BR>        Try<BR>            pWorkspace = pWorkspaceFact.Open(pPropertySet, 0)<BR>            pFeatureWorkspace = pWorkspace<BR>            Dim pFeaturelayer As IFeatureLayer = New FeatureLayer<BR>            pFeaturelayer.FeatureClass = pFeatureWorkspace.OpenFeatureClass("sde.dbo.gzcity_region")<BR>            Return (pFeaturelayer)<BR>        Catch ex As System.Exception<BR>            MsgBox("error:" + ex.Message)<BR>        End Try<BR>    End Function</P>
<P>End Class<BR></P>
<img src="images/post/smile/dvbbs/em12.gif" />

<P>用.net的esri的自动引用工具，把engine的库都引上，看是否能用</P>