facebook login issue

If enable the facebook account in settings, when change account can't open the session.

-(void)fbResync
{
    ACAccountStore *accountStore;
    ACAccountType *accountTypeFB;
    if ((accountStore = [[ACAccountStore alloc] init]) && (accountTypeFB = [accountStore accountTypeWithAccountTypeIdentifier:ACAccountTypeIdentifierFacebook] ) ){

    NSArray *fbAccounts = [accountStore accountsWithAccountType:accountTypeFB];
    id account;
    if (fbAccounts && [fbAccounts count] > 0 && (account = [fbAccounts objectAtIndex:0])){

    [accountStore renewCredentialsForAccount:account completion:^(ACAccountCredentialRenewResult renewResult, NSError *error) {
        //we don't actually need to inspect renewResult or error.
        if (error){

        }
    }];
}
}

[FBSession openActiveSessionWithReadPermissions:permissions
                                   allowLoginUI:YES
                              completionHandler:^(FBSession *session, FBSessionState state, NSError *error) {
     if(error)
     {
         NSLog(@"Session error");
         [self fbResync];
         [NSThread sleepForTimeInterval:0.5];   //half a second
         [FBSession openActiveSessionWithReadPermissions:permissions
                                            allowLoginUI:YES
                                       completionHandler:^(FBSession *session, FBSessionState state, NSError *error) {
            [self sessionStateChanged:session state:state error:error];
                                       }];

     }
     else
         [self sessionStateChanged:session state:state error:error];
 }];