objective c - iOS: Nonexistent Pointer is Crashing App -

when open specific storyboard scene, app crashes error: "incorrect checksum freed object - object modified after being freed". i've got "exc_bad_access" crashes going on, it's 1 or other. couldn't find troubled pointer, tested out nszombieenabled. lead me message on crash: *** -[nscontentsizelayoutconstraint seconditem]: message sent deallocated instance 0x1e0a5220

now, searched project [nscontentsizelayoutconstraint seconditem], , nscontentsizelayoutconstraint , seconditem individually. exists in project. i'm still new objective-c, , have no idea next. also, run fine 1 out of 5 times on device , simulator. happened with: -[nsattributedictionary release]:, no in project either. also, *** -[pitchdetector addsamples:innumberframes:]:. keep changing, , can't find these anywhere in project. , runs fine sometimes, on simulator, makes frustrating since error keeps changing on device when crashes.

to switch views in storyboard, i'm using code. in viewdidload on main screen: x1viewcontroller = [[uistoryboard storyboardwithname:@"main" bundle:nil] instantiateviewcontrollerwithidentifier:@"x1viewcontroller"];

and when button pushed load it: - (ibaction)button4:(id)sender { [self presentviewcontroller:x1viewcontroller animated:yes completion:nil]; }

i've set other page transitions exact same way , switch on fine. troubled one.

here stack trace:

and here weird thing found during analysis i'm unsure of how fix:

update: i'm getting message "error: 1768843636" in console once page loads. strange.

to switch views in storyboard, i'm using code. in viewdidload on main screen:

x1viewcontroller = [[uistoryboard storyboardwithname:@"main" bundle:nil]                          instantiateviewcontrollerwithidentifier:@"x1viewcontroller"]; 

well, there's problem. viewdidload way soon. aren't in interface yet , trying move next state of interface. moreover, running risk of trying present same view controller instance on different occasions.

move code button-press code. don't need view controller instantiated until moment comes when present it. use new view controller instance each time present.