Getting problem to wall post on Facebook

When I login to Facebook through my app, everything works, but I'm having problems posting to walls.

- (NSString *) postToFBWallStatus:(NSString *) status andSetDelegate: (id) delegate
{
    if (! isFBLoggedIn) 
    {
        return @"NotLoggedin";
    }

    NSString *message = status;
    NSLog(@"Appdelegate: postToFBWallStatus:andSetDelegate:");
    NSLog(@"to be delegate class: %@",[delegate class]);

    NSURL *url = [NSURL URLWithString:@"https://graph.facebook.com/me/feed"];

    ASIFormDataRequest *newRequest = [ASIFormDataRequest requestWithURL:url];
    [newRequest setPostValue:message forKey:@"message"];
    [newRequest se开发者_运维知识库tPostValue:@"" forKey:@"name"];
    [newRequest setPostValue:@"" forKey:@"caption"];
    [newRequest setPostValue:@"" forKey:@"description"];
    [newRequest setPostValue:@"" forKey:@"link"];
    [newRequest setPostValue:@"" forKey:@"picture"];
    [newRequest setPostValue:_accessToken forKey:@"access_token"];
    [newRequest setDidFinishSelector:@selector(postToWallFinished:)];
    [newRequest setDidFailSelector:@selector(postToWallFailed:)];
    [newRequest setDelegate:delegate];
    [newRequest startAsynchronous];

    return @"Loggedin";
}

I get this message when I post to the Facebook wall:

error =     {
        message = "Invalid access token signature.";
        type = OAuthException;
    };

You must use the user's access_token to post information to their wall. Furthermore, the user needs to allow the publish_stream permission for the API call to work. When you authenticate the user, add publish_stream to the scope of permissions.