Unit of work is not associated with a LightSpeedContext

I'm using LightSpeed O/R Mapper in VS2012,with .net 4.0

when I creat an lsmodel with sqlite 3.0 database ,connected successfully, then I drag some tables into the lsmodel diagram design,it still seems normal. but when I using linq ,some error occurs:Unit of work is not associated with a LightSpeedContext? why it happens,how can i solve it?Thanks a lot. here's my C# code:

    private void button1_Click(object sender, EventArgs e)
    {
        SQLMUnitOfWork model = new SQLMUnitOfWork();
        var sum1 = from c in model.Cs select c;
        var sum = from c1 in model.Scs join c2 in model.s on c1.Sno equals c2.Sno join c3 in model.Cs on c1.Cno equals c3.Cno select new{SNO=c1.Sno,SN=c2.Sn,SEX=c2.Sex,AGE=c2.Age,CNO=c1.Cno,CN=c3.Cn,CT=c3.Ct,SCORE=c1.Score};
        c1TrueDBGrid1.DataSource = sum1;
        c1TrueDBGrid1.SetDataBinding();
    }

neighter sum1 nor sum works.

You need to create a UnitOfWork from a LightSpeedContext rather than new'ing one up. e.g.

using (var model = new LightSpeedContext<SQLMUnitOfWork>("Development").CreateUnitOfWork())
{
    var sum1 = from c in model.Cs select c;
    var sum = from c1 in model.Scs join c2 in model.s on c1.Sno equals c2.Sno join c3 in model.Cs on c1.Cno equals c3.Cno select new{SNO=c1.Sno,SN=c2.Sn,SEX=c2.Sex,AGE=c2.Age,CNO=c1.Cno,CN=c3.Cn,CT=c3.Ct,SCORE=c1.Score};
    c1TrueDBGrid1.DataSource = sum1;
    c1TrueDBGrid1.SetDataBinding();
}

Jeremy