'NSFetchedResultsController does not support both change tracking and fetch request's with NSDictionaryResultType'

I have an application that was running just fine under OS3+. But it does not work under OS4. I get the following error message:

'NSFetchedResultsController does not support both change tracking and fetch request's with NSDictionaryResultType'

Does it ring a bell to anyone here?

- (NSFetchedResultsController *)fetchedResultsController {

    if (fetchedResultsController != nil) {
        return fetchedResultsController;
    }

    /*
     Set up the fetched results controller.
     */
    // Create the fetch request for the entity.
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    // Edit the entity name as appropriate.
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"myEntity" inManagedObjectContext:managedObjectContext];

    [fetchRequest setEntity:myEntity];

    [fetchRequest setResultType:NSDictionaryResultType];

    [fetchRequest setPropertiesToFetch :[NSArray arrayWithObjects:@"FIELD1",@"FIELD2",@"FIELD3",@"FIELD4",@"FIELD5",nil]];      

    // Setting unique values        
    [fetchRequest setReturnsDistinctResults:YES];       

    // Edit the sort key as appropriate.
    NSSortDescriptor *initialDescriptor = [[NSSortDescriptor alloc] initWithKey:@"FIELD1" ascending:YES];

    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:initialDescriptor, nil];

    [fetchRequest setSortDescriptors:sortDescriptors];      

    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".       
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:@"FIELD1" cacheName:@"myCache"];

    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;
    [aFetchedResultsController release];
    [fetchRequest release];
    [initialDescriptor release];
    [sortDescriptors release];      

    return fetchedResultsController;
}    

Thanks in advance.