关于IOS5中pdf添加到Email中

添加一个pdf到Email中，操作如下：

-(IBAction)mailPDF:(id)sender{
    MFMailComposeViewController* controller = [[MFMailComposeViewController alloc] init];
    controller.mailComposeDelegate = self;
    NSLog(@"myData is %@",myData);
    [controller setSubject:@"Geselecteerde favorieten van Genk on Stage"];
    [controller setMessageBody:@"<p>Hallo muziekliefhebber <br /> In bijlage vind je jouw favorieten. Volg en praat met ons mee op facebook.com/genkonstage of @genkonstage!<br /> Veel plezier op Genk on stage! </p>" isHTML:YES];
    if (controller){
        [self presentModalViewController:controller animated:YES];
        [controller addAttachmentData:myData mimeType:@"application/pdf" fileName:@"favorite.pdf"];
    }else{
        NSLog(@"nothing to show");
    }
}

设置数据：

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *filePath = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"favorite.pdf"];
 myData = [NSData dataWithContentsOfFile: filePath];

在看log mydata（就是pdf）时，显示并不为空。浏览模拟器“我的文档”也能看见pdf。
请指教为什么我的pdf无法添加到Email中?

在ios6中没问题，只有在ios5中有问题。