Please contact forumrunner.com for app support. GC deals with forum related issues, whereas the app is maintained by a separate company. They have a whole forum for support, so you should be able to find answers there.
There is an iPhone app: http://itunes.apple.com/us/app/grasscity-forum/id427699719 And an Android app, too: https://market.android.com/details?id=net.endoftime.android.forumrunner.grasscity Both free