ios - Rerequesting the Publish Permission -

i have problem when re- request publish permission (manage_notifications) after getting readpermission.

the use case if read permission asks user authorize manage_notifications permission if user don't allow , try again next time app crashes saying

terminating app due uncaught exception 'com.facebook.sdk:invalidoperationexception', reason: 'fbsession: not valid reauthorize while previous reauthorize call has not yet completed.' 

i checking fbsession open before requesting publish permissions.

below code

 if([[fbsession activesession] isopen] ){  if ([fbsession.activesession.permissions indexofobject:@"manage_notifications"] == nsnotfound) {         // if don't have permission, request          [fbsession.activesession  requestnewpublishpermissions:@[@"manage_notifications"]                                               defaultaudience:fbsessiondefaultaudienceonlyme                                             completionhandler:^(fbsession *session, nserror *error) {                                                  if (!error) {                                                     alog(@"requesting new permission");                                                  } else{                                                     nsstring *mytitle = @"";                                                     nsstring *body = @"";                                                      if ( [fberrorutility errorcategoryforerror:error ] == fberrorcategoryusercancelled) {                                                         mytitle = @"permission denied";                                                         body = @"unable permission notifications.";                                                     }  if([fberrorutility errorcategoryforerror:error  ] == fberrorcategorypermissions){                                                         mytitle = @"permission denied";                                                         body = @"unable permission notifications.";                                                      }else {                                                          mytitle = @"permission error";                                                         body = @"unable permission notifications.";                                                     }                                                     uialertview *alertview = [[uialertview alloc] initwithtitle:mytitle                                                                                                         message:body                                                                                                        delegate:nil                                                                                               cancelbuttontitle:@"ok"                                                                                               otherbuttontitles:nil];                                                     [alertview show];                                                    }                                               }];     } }