方法一、下载SQL Server Compact 4.0 安装后就可以解决。下载地址是：
http://www.microsoft.com/downloads/zh-cn/details.aspx?familyid=033cfb76-5382-44fb-bc7e-b3c8174832e2&displaylang=zh-cn
方法二、在web.config里添加
<system.data>
<DbProviderFactories>
<add name="MySQL Data Provider" invariant="MySql.Data.MySqlClient" description=".Net Framework Data Provider for MySQL" type="MySql.Data.MySqlClient.MySqlClientFactory,MySql.Data" />
</DbProviderFactories>
</system.data>