Select multiple records based on List of strings with LINQ

I have looked at similar question - ids not string - but it wont work for me so I am reposting.

Store model:

public class Store
{
    public int ID { get; set; }

    public virtual IList<Asset> Assets { get; set; }
}

Till:

public class Till
{
    public int ID { get; set; }

    [ForeignKey("Store")]
    public int StoreID { get; set; }
    public virtual Store Store { get; set; }

    public int Type { get; set; }
    public string Kind { get; set; }
    public string Name { get; set; }
}

Using MvcCheckBoxList reference library I have a FilterViewModel containing list of names:

public class FilterViewModel
{
    public IEnumerable<TillCheckBox> AvailableTills { get; set; }
    public IEnumerable<TillCheckBox> SelectedTills { get; set; }
    public PostedTills PostedTills { get; set; }
}

public class PostedTills
{
    public string[] TillNames { get; set; }
}

The FilterViewModel.AvailableTills is initialised with the names of all assets of type Till (eg. { "Front", "Back", "Floor", "Shop", "Cafe" }):

private List<string> GetAllTills()
{
    return (from a in _db.Assets where (a.Kind == "Till") select a.Name).Distinct().ToList();
}

The FilterViewModel.SelectedTills and FilterViewModel.PostedTills are both empty. Nothing selected yet.

When the View uses FilterViewModel and when submits back via GET a list of selected checkboxes back to the controller in FilterViewModel .

What I am trying to do is get list of stores which have assets with name in PostedTills list.

So if user selects "Front" and "Cafe" I want stores which has assets named "Front" AND "Cafe".

Instead what I am getting is a list of stores with assets named "Front" (but not necessarily "Cafe") and assets named "Cafe" (but not "Front").

The Linq query I am trying (based on other post) is:

stores = (from s in db.Stores
join a in db.Assets on s.ID equals a.StoreID
where (a => postedTillNames.Contains(a.Name))
select s).Distinct().ToList();

But this gives an error "Cannot convert lambda expression to type 'bool' because it is not a delegate type" on:

(a => postedTillNames.Contains(a.Name))

I have also tried different queries but cannot get the results I am after.

Anyone able to help please?

Regards Craig