UIDocument openWithCompletionHandler returns NO for success

I have this code:

[metaDoc openWithCompletionHandler:^(BOOL success) {
    if (!success) {
        NSLog(@"UH OH");
    }
}];

Why would it ever return NO? For me, this returns NO, although in my

- (BOOL)loadFromContents:(id)contents 
                  ofType:(NSString *)typeName 
                   error:(NSError **)outError 

I always return YES.

thank