先判断presentedViewController为空时，再presentModalViewController
if (self.presentedViewController == nil)
{
[self presentModalViewController:myController animated:YES];
}
模态窗口错误 Application tried to present modally an active controller,布布扣,bubuko.com
模态窗口错误 Application tried to present modally an active controller
原文：http://blog.csdn.net/sqc3375177/article/details/22172859