“应为ResourceDictionary的继承者”-此错误是什么意思

在App.xaml中,我有以下代码:

<Application
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    x:Class="FJW.App">
    <Application.Resources>
        <!-- Resources scoped at the Application level should be defined here. -->
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="themes/F4.xaml"/>
                <ResourceDictionary Source="themes/F3.xaml"/>
                <ResourceDictionary Source="themes/F2.xaml"/>
                <ResourceDictionary Source="themes/F0.xaml"/>
                <ResourceDictionary Source="themes/F1.xaml"/>
                <ResourceDictionary Source="themes/Palm.xaml"/>
                <ResourceDictionary Source="themes/Key.xaml"/>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>

Visual Studio在字符串中发现错误 <ResourceDictionary Source="themes/...xaml"/> 需要ResourceDictionary的继承者。

但该项目正在正确编译,并且工作正常。错误消息是什么意思?也许这是这个Silverlight测试版的一个bug?还是我的错?