How to correctly instantiate a PopoverController - iphone

Question

I have a SplitviewController with multiple possible Detailviews (Webviews, Tableviews, regular UIViews).
As an example, I have a NavigationController on top, then navigate through some tables.
Finally I show some Content, lets say a UIWebview. I rotate the iPad to portrait, and in the toolbar I add a Button from which the popOverController is displayed.
On Buttonclick I say:
if (!popoverController) {
if (self.view.window != nil) {
popoverController = [[UIPopoverController alloc] initWithContentViewController: [appDelegateiPad naviPad]];
popoverController.delegate = self;
}
}
Here, I instantiate a PopOverController and the Content is the left part of the splitview, from the point I left off. All is nice.
But when I rotate, I get this warning:
CoreAnimation: ignoring exception: Popovers cannot be presented from a view which does not have a window.
And on the screen the popOverController reappears with empty content (black translucent I would say) but I don't know why, since I dismissed it and there cant be another instance since I only create one on buttonclick.
This has been driving me crazy for days.
ANY(!) help is appreciated!
-(void) showPopOver:(id) sender {
NSLog(#"showing popover?");
if (!popoverController) {
if (self.view.window != nil) {
popoverController = [[UIPopoverController alloc] initWithContentViewController:[appDelegateiPad naviPad]];
//RootViewController *r = [[RootViewController alloc] initWithNibName:#"RootViewController" bundle: nil];
// popoverController = [[UIPopoverController alloc] initWithContentViewController:r];
//popoverController.popoverContentSize = CGSizeMake(320, 800);
//popoverController.delegate = self;
}
}
if (![popoverController isPopoverVisible]) {
[popoverController presentPopoverFromBarButtonItem:barButton3 permittedArrowDirections:UIPopoverArrowDirectionAny animated:YES];
//[popoverController presentPopoverFromRect:CGRectMake(10, 10, 20, 20) inView:self.view permittedArrowDirections:UIPopoverArrowDirectionRight animated:YES];
}
else {
[popoverController dismissPopoverAnimated:NO];
}
}