How to avoid unrecognised selector sent to NSCFArray sortUsingDescriptor: in iphone?

I am new to iphone development .I am trying to sort a NSMutable array with reference to the date which is saved as object for the key "pubDate".After parsing the url i am saving the date as date format in an array"myPubDate".

 (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string{
//NSLog(@"found characters: %@", string);
// save the characters for the current item...
if ([currentElement isEqualToString:@"title"]) {
    [currentTitle appendString:string];
} else if ([currentElement isEqualToString:@"link"]) {
    [currentLink appendString:string];
} else if ([开发者_开发百科currentElement isEqualToString:@"description"]) {
    [currentSummary appendString:string];
} else if ([currentElement isEqualToString:@"pubDate"]) {
    [currentDate appendString:string];
    NSDateFormatter *df =[[NSDateFormatter alloc] init];
    [df setFormatterBehavior:NSDateFormatterBehavior10_4];
    [df setDateFormat:@"EEE, dd MMM yyyy"];
    myPubDate = [df dateFromString:currentDate];

}


  - (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName{     
//NSLog(@"ended element: %@", elementName);
if ([elementName isEqualToString:@"item"]) {
        [item setObject:currentTitle forKey:@"title"];
            [item setObject:currentLink forKey:@"link"];
            [item setObject:currentSummary forKey:@"description"];
            [item setObject:myPubDateforKey:@"pubDate"] 

            [item setObject:currentImage forKey:@"imagePath"];
            NSLog(@"Befor if condition");
            [stories addObject:[item copy]];
        }
                        recent = [stories copy];}

 For sorting
    NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:@"pubDate" ascending:NO]; 
    [recent sortUsingDescriptor:[NSArray arrayWithObjects:descriptor, nil]];  
 recent1 = [recent sortedArrayUsingDescriptors:descriptor];
[descriptor release];

I am geeting an error in the console as

[NSCFArray sortUsingDescriptor:]: unrecognized selector sent to instance 0x4ed10c0

Where do i go wrong? please help me out.Thanks.

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Your problem appears to be a typo: sortUsingDescriptor: is not the same as sortUsingDescriptors: