Table not in List to Append to

I must be missing something really obvious, but I want to append some
rows to a table I've created, but when I change my query type to
Append, the list of tables I can choose to append to omits the table I
want, while showing the others.

The one I want to append to does appear if I try to show a table to
select from (but it has nothing in it yet).

What could prevent the table from being available to append to?

Thanks.