提供程序未返回 ProviderManifestToken 字符串。

连接字符串写错导致，修改后OK。

原来的：
 <connectionStrings>
    <add name="EFDbContext" connectionString="Data Source=Brian-PC-c;Initial Catalog=SportsStore;Persist Security Info=True;User ID=sa;Password=global"
  providerName="System.Data.SqlClient"/>


  </connectionStrings>

修改后的：
 <connectionStrings>
    <add name="EFDbContext" connectionString="Data Source=Brian-PC;Initial Catalog=SportsStore;Persist Security Info=True;User ID=XXX;Password=XXX"
  providerName="System.Data.SqlClient"/>


  </connectionStrings>