No entiendo por qué este código no se compilará

ExecutorService executor = new ScheduledThreadPoolExecutor(threads);

class DocFeeder implements Callable<Boolean> {....} 
... 
List<DocFeeder> list = new LinkedList<DocFeeder>();
list.add(new DocFeeder(1));
...
executor.invokeAll(list);

El mensaje de error es:

The method invokeAll(Collection<Callable<T>>) in the type ExecutorService is 
not applicable for the arguments (List<DocFeeder>)  

list es unCollection deDocFeeder, que implementaCallable<Boolean> - ¡¿Que esta pasando?!