Answer by Jeff Mercado for LINQ to XML query from multiple ListBox items

Try changing your where clause like so:

.Where(b => lbxItems.Items    .Cast<ListItem>() // needs a cast    .Where(i => i.Selected)    .Select(i => i.Value)    .Contains(b.Element("Category").Value))

The idea is to determine what items are selected and see if your category value is among those selected.