Newer version (the real EF5) is dependent on .NET 4.5. If you have added EF5 when your project was based on .NET 4.0 you will have only EF 4.4 (EF5 version without features dependent on .NET 4.5). After upgrading to EF 5.0 you need to update EntityFramework package. You can try to use Update-Package command. If it doesn’t help you will need to uninstall package first and than add it again.