Thanks. I've got it running now.

>>

>>var openInvoices = (List < D010Invoices.Invoice > )D010Invoices.invoices.Select(i => i.paid == false).;
>>

>>
>>if D010Invoices.invoices is a List of D010Invoice.Invoice why can't openInvoices be cast to it?
>
>The linq is going to return a Boolean IEnumerable. Use:

D010Invoices.invoices.Where(i => i.paid == false);

That will give you an IEnumerable of Invoices. If you need a List then tack on the .ToList() as Craig suggested.
>
>Tip: If you are using var then omit the cast and hover over 'var' - that will show the type which the linq would return.