EF codefirst 更新表的问题，遇到以下问题该怎么解决,提示 Type is not resolved for member 'MySql

Question

 Update-Database -Script -ProjectName "Mem.Data" -StartUpProjectName "Mem.Admin.UI" -ConnectionStringName "DataContext"  -Force
No pending explicit migrations.
Applying automatic migration: 201404181711012_AutomaticMigration.
PM> Update-Database -ProjectName "Mem.Data" -StartUpProjectName "Mem.Admin.UI" -ConnectionStringName "DataContext"  -Force
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
No pending explicit migrations.
Applying automatic migration: 201404181711254_AutomaticMigration.
System.Runtime.Serialization.SerializationException: Type is not resolved for member 'MySql.Data.MySqlClient.MySqlException,MySql.Data, Version=6.8.3.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d'.
   在 System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate)
   在 System.Data.Entity.Migrations.Design.ToolingFacade.Run(BaseRunner runner)
   在 System.Data.Entity.Migrations.Design.ToolingFacade.Update(String targetMigration, Boolean force)
   在 System.Data.Entity.Migrations.UpdateDatabaseCommand.<>c__DisplayClass2.<.ctor>b__0()
   在 System.Data.Entity.Migrations.MigrationsDomainCommand.Execute(Action command)
Type is not resolved for member 'MySql.Data.MySqlClient.MySqlException,MySql.Data, Version=6.8.3.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d'.