xcode4 - NSException error seems to occur randomly

Question

This code was working fine, now for some reason I'm getting an NSException error that's generating a SIGABRT at the following line of code...

 self.popoverController = [[[UIPopoverController alloc] initWithContentViewController:wbPopOverController] autorelease];

Here's the method it's located in...

-(IBAction)showPop:(id)sender {

//close any open popovers
[self.popoverController dismissPopoverAnimated:NO];

// Initialize wbPopUpViewController
PopoverAircraftClass *wbPopOverController = [[PopoverAircraftClass alloc] initWithNibName:@"PopoverAircraftClass" bundle:[NSBundle mainBundle]];
wbPopOverController.contentSizeForViewInPopover = CGSizeMake(175, 216);
wbPopOverController.delegate = self; //for update    

[wbPopOverController setAircraftList:aircraftList withCurrentValue:activeRegistration];

// Object converted to UIPopOverController (retained so we can reference it)
self.popoverController = [[[UIPopoverController alloc] initWithContentViewController:wbPopOverController] autorelease];
self.popoverController.passthroughViews = [NSArray arrayWithObject: self.view];

[self.popoverController presentPopoverFromRect:[sender frame] inView:self.layoutViewIB permittedArrowDirections:UIPopoverArrowDirectionUp animated:NO];
[wbPopOverController release];
}

I'm new at this as you can probably tell. Any ideas as to what's generating the NSException?