以程序方式创建应用程序池，错误设置“；ManagedPipelineMode”；

我正在使用以下代码以编程方式为IIS 6（Windows Server 2003R2）创建应用程序池，但在尝试设置ManagedPipelineMode 的行上出现错误

尝试1

        string metabasePath = @"IIS://localhost/W3SVC/AppPools";
        DirectoryEntry apppools = new DirectoryEntry(metabasePath);
        DirectoryEntry newpool = apppools.Children.Add(AppPoolName, "IIsApplicationPool");
        newpool.Properties["managedRuntimeVersion"].Value = "v4.0";
        newpool.InvokeSet("ManagedPipelineMode", new Object[] { 0 }); //exception thrown on this line
        newpool.Properties["Enable32BitAppOnWin64"].Value = true;
        if (!string.IsNullOrEmpty(username))
        {
            newpool.Properties["AppPoolIdentityType"].Value = 3;
            newpool.Properties["WAMUserName"].Value = username;
            newpool.Properties["WAMUserPass"].Value = password;
        }
        newpool.CommitChanges();

尝试2

        string metabasePath = @"IIS://localhost/W3SVC/AppPools";
        DirectoryEntry apppools = new DirectoryEntry(metabasePath);
        DirectoryEntry newpool = apppools.Children.Add(AppPoolName, "IIsApplicationPool");
        newpool.Properties["managedRuntimeVersion"].Value = "v4.0";
        newpool.Properties["ManagedPipelineMode"][0] = 0; //exception thrown on this line
        newpool.Properties["Enable32BitAppOnWin64"].Value = true;
        if (!string.IsNullOrEmpty(username))
        {
            newpool.Properties["AppPoolIdentityType"].Value = 3;
            newpool.Properties["WAMUserName"].Value = username;
            newpool.Properties["WAMUserPass"].Value = password;
        }
        newpool.CommitChanges();

无论哪种方式都会引发相同的异常。

异常：

Exception from HRESULT: 0x80005006
    at System.DirectoryServices.Interop.UnsafeNativeMethods.IAds.PutEx(Int32 lnControlCode, String bstrName, Object vProp)
    at System.DirectoryServices.PropertyValueCollection.OnClearComplete()
    at System.DirectoryServices.PropertyValueCollection.set_Value(Object value)