GameCenter Operation cancelled if account never used with game center - iphone

Question

I am using GameCenter on my app. I have these lines
GKLocalPlayer *localPlayer = [GKLocalPlayer localPlayer];
[localPlayer authenticateWithCompletionHandler:^(NSError *error) {
if (localPlayer.isAuthenticated)
{
}
the problem is that the localPlayer.isAuthenticated flag is always TRUE bur error variable comes with code 2 = "operation was cancelled" (???).
I have sign out from device's game center and from the store but this flag is always true and I do not see the game center sign in that my app should show when it starts. I don't see either the "welcome" banner that always show when a game that uses game center starts.
How do I force a sign out of game center to make the sign in window to show again?
I am compiling for iOS 4.3.
thanks
What I have discovered now is that this happens if you never signed in on device's game center. Once you login there, and say you want to use your username on game center, the app works. The worst part is this: suppose someone downloads the game but does not have the game center set yet. So, the game will never work for them? My game is supposed to work exclusively with game center on. So, for me this is an issue.

Answer 1

For me its working great. Just changed code from
if([GKLocalPlayer localPlayer].authenticated)
To
if([GKLocalPlayer localPlayer].authenticated == NO)
//Other codes
if([GKLocalPlayer localPlayer].authenticated == NO)
{
[[GKLocalPlayer localPlayer] authenticateWithCompletionHandler:^(NSError *error)
{
[self processGameCenterAuth: error];
}];
}
- (void) processGameCenterAuth: (NSError*) error
{
if(error == NULL)
{
[mGameCenterManager reloadHighScoresForCategory: self.currentLeaderBoard];
}
else
{
// NSLog(#"%#\n\n",[NSString stringWithFormat: #"Reason: %#", [error localizedDescription]]);
AppController *app = (AppController*)[UIApplication sharedApplication].delegate;
if(!app.isgameCenterStarted)
{
UIAlertView* alert= [[[UIAlertView alloc] initWithTitle:#"Game Center Unavailable" message: #"Player is not signed in"
delegate: NULL cancelButtonTitle: #"OK" otherButtonTitles: NULL] autorelease];
[alert show];
}
else
{
[[NSNotificationCenter defaultCenter] postNotificationName:#"GameCenterUnAvailable" object:nil];
}
}
}