Until iOS7 update I was using...
UIImage *image = [moviePlayer thumbnailImageAtTime:1.0 timeOption:MPMovieTimeOptionNea
Jeely provides a good work around but it requires an additional library that isn't necessary when the MPMoviePlayer already provides functions for this task. I noticed a syntax error in the original poster's code. The thumbnail notification handler expects an object of type NSNotification, not a dictionary object. Here's a corrected example:
-(void)MPMoviePlayerThumbnailImageRequestDidFinishNotification: (NSNotification*)note
{
NSDictionary * userInfo = [note userInfo];
UIImage *image = (UIImage *)[userInfo objectForKey:MPMoviePlayerThumbnailImageKey];
if(image!=NULL)
[thumbView setImage:image];
}