Cannot remove an entity that has not been attached.

You will not be able to use attach on a context other then the original context the item was received on unless the entity has been serialized.

public bool deleteslabrecord(TSummeryReport deletetsr)
{
EntityManager.TSummeryReports.DeleteOnSubmit(EntityManager.TSummeryReports.Single(theItem=>theItem==deletetsr));
return SaveChanges();
}