LINQ Lambda Join Error - cannot be inferred from the usage

I had troubles joining two DbSets and continued to receive the "cannot be inferred error". I struggled to find a solution so I thought I would share my simple answer. There are several great posts from Jon Skeet and others but most of the answers were over my head.

Here is the code that was causing me trouble:

using(var db = new SomeDataContext())
    {
    db.DemandData
        .Where(demand=> demand.ID == SearchID)
        .Join(db.CUST_ORDER_LINE,
            supply=> new { supply.LINE, supply.SALES_ORDER_ID },
            demand=> new { demand.LINE_NO, demand.CUST_ORDER_ID },
            (supply, demand) => new { custOrderLineReturn = demand })
        .Select(s => s.custOrderLineReturn )
        .ToList();
    }