Splitview中的UIActionsheet与iOS 5.1更新崩溃

从5.0更新到iOS 5.1后,从splitview控制器的弹出窗口中的按钮显示的操作表正在使应用程序崩溃.它输出的错误是：*断言失败 – [UIActionSheet presentSheeTinPopoverView：],/ sourceCache / UIKit / UIKit-1914.84 / UIActionSheet.m：1816
所以在Splitview控制器的主视图中,我有一个相机按钮,我试图提出一个动作表,要求从相机胶卷或相机中选择.有任何想法吗？

if(lpm != null)  //Long Press Menu / Action Sheet
    lpm = null;
lpm = new UIActionSheet("SELEct an action to perform on " + Application.MO.CurrentList[indexPath.Row].Name);
foreach(var button in buttonList)
    lpm.AddButton(button);
lpm.CancelButtonIndex = buttonList.Count - 1;
lpm.Style = UIActionSheetStyle.blackTranslucent;                
lpm.ShowFrom(tHelist.RectForRowATindexPath(indexPath),this.View,truE);
lpm.Clicked += delegate(object sender,UIButtonEventArgs e2) {
                    lpm.DismissWithClickedButtonIndex(e2.buttonIndex,falsE);
                            Application.MO.RespondToLongPressSelection(e2.buttonIndeX);
                        };

if (UIInterfaceOrientationIsPorTrait([UIApplication sharedApplication].statusBarOrientation))
        [sortSheet showInView:self.view.window];
    else
        [sortSheet showFromBarButtonItem:sender animated:YES]; // rightBarButton