In migrating my website from Asp.Net 3.5 to 4, I got this error.

The type or namespace name 'Objects' does not exist in the namespace 'System.Data'

Objects did not resolve in this using statement.

using System.Data.Objects

My website uses Linq to Sql.

Had to add a reference in web.config to System.Data.Entity. Also added a reference to the System.Data.Linq.

<add assembly="System.Data.Linq, Version=4.0.0.0, ...
<add assembly="System.Data.Entity, Version=4.0.0.0, ...