Problems with NSMutableDictionary and NSMutableArray ( Mutating Error - but why? )

Question

Solution: Make the NSArray mutable with mutableCopy

I want to edit a NSDictionary in a NSArray in NSUserDefaults. That's a bigger problem than I thought :/ The property parentpop.dataseditable is (retain, nonatomic) and loads the NSArray with the code

dataseditable = (NSMutableArray*)[[NSUserDefaults standardUserDefaults]arrayForKey:(@"array")];

so there should be really no problem. I hope you can help me.

//  EditSUPER.m
//  HITS Datenbank
//
//  Created by Jonathan Lucas Fritz on 02.05.16.
//  Copyright © 2016 NOSCIO. All rights reserved.
//

#import "EditSUPER.h"
NSString *key_edit;
NSString *index_edit;
NSMutableDictionary *dica4;
UITextView *textview;
@implementation EditSUPER
-(void)loadandsavefor:(NSString *)key andindex:(NSString *)index
{
    self.backgroundColor = [UIColor blackColor];
    key_edit = key;
    index_edit = index;

    UIButton *back;
    UIButton *save;
    textview = [[UITextView alloc]initWithFrame:CGRectMake(0, 40, self.frame.size.width, self.frame.size.height-40)];
    textview.backgroundColor = [UIColor whiteColor];
    back = [[UIButton alloc]initWithFrame:CGRectMake(0, 0, 150, 40)];
    save = [[UIButton alloc]initWithFrame:CGRectMake(self.frame.size.width-160, 0, 150, 40)];

    [back setTitle:(@"Zurück") forState:UIControlStateNormal];
    [save setTitle:(@"Speichern") forState:UIControlStateNormal];
    [save setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
    [back setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
    [save setTitleColor:[UIColor whiteColor] forState:UIControlStateHighlighted];
    [back setTitleColor:[UIColor whiteColor] forState:UIControlStateHighlighted];
    [self addSubview:textview];
    [self addSubview:back];
    [self addSubview:save];
    [save addTarget:self action:@selector(savethat) forControlEvents:UIControlEventPrimaryActionTriggered];
    [back addTarget:self action:@selector(cancelediting) forControlEvents:UIControlEventPrimaryActionTriggered];

    dica4 = (NSMutableDictionary*)[self.parentpop.dataseditable objectAtIndex:index.intValue];
//    dica4 = (NSMutableDictionary*)_usethisdic;
    textview.text = [dica4 valueForKey:key_edit];

}
-(void)savethat //Save the Users Input and replace the old
{
    [textview resignFirstResponder];
    [dica4 setValue:textview.text forKey:key_edit];
    printf("\n %d ",index_edit.intValue);
    [_parentpop.dataseditable replaceObjectAtIndex:index_edit.intValue withObject:dica4];

    [[NSUserDefaults standardUserDefaults] setObject:_parentpop.dataseditable forKey:(@"array")];
    [[NSUserDefaults standardUserDefaults]synchronize];

    [self.parentpop removeFromSuperview];
//    [self.intclasssecond reloadData];

}
-(void)cancelediting //Cancel
{
    [textview resignFirstResponder];
    [self.parentpop removeFromSuperview];
}
@end