Exception thrown when deleting node from doubly linked list

[N1A5SL3A]

Hello! I am currently removing similar strings of two doubly linked lists. This function is partly working. It seems to only run into an error when I have to delete two elements in a row. Therefore I think I and not handling the "prev" pointer correctly. If you see anything wrong I would really appreciate the help.

Here is the class header:

#ifndef DBLLINKEDLIST_H
#define DBLLINKEDLIST_H
#include "stdafx.h"
#include <string>
#include "DString.h"

using namespace std;
class Node {
public:
	Node() {
		next = prev = nullptr;
	}
	Node(CDString str) {
		data = str;
		next = prev = nullptr;
	}
	CDString data;
	Node *next;
	Node *prev;
};
class DblLinkedList {
public:

	DblLinkedList();
	void push_back(const CDString& str);
	void resetIterator() const;
	bool hasMore() const;
	CDString next() const;
	void testConnections();
	DblLinkedList(const DblLinkedList& dll);
	void operator =(const DblLinkedList& dll);
	DblLinkedList::~DblLinkedList();
	int getCount();
	bool remove(const DblLinkedList & arg);

	bool insert(const CDString& str);

	friend ostream& operator << (ostream& left, DblLinkedList right);

private:
	Node *head, *tail;
	mutable Node *it;      // mutable says that it can change in a const member function
	int count;
};
#endif

Here is the function I am having trouble with:

bool DblLinkedList::remove(const DblLinkedList & arg)
{
	CDString strTemp;
	DblLinkedList listTemp;
	Node *temp;
	
	listTemp = arg;
	listTemp.it = listTemp.head;
	it = head;

	do 
	{
		do
		{
			if (it == nullptr)
			{
				it = head;
				//it->prev = nullptr;
			}
			if (it->data == listTemp.it->data)
			{
				it->prev->next = it->next;
				it->next->prev = it->prev;
				it = it->next;
				if (it->prev == head)
				{
					head = it;
				}

				delete it->prev;
				count--;
				cout << "Removed: " << listTemp.it->data << endl;
			}
			else
			{
				it = it->next;

			}
		} while (!(it == nullptr));

		listTemp.it = listTemp.it->next;
	} while (listTemp.it != nullptr);    //removed next
	{
		cout << "Removal completed\n";
		return true;
	}
}

I have two successful removes, and then an exception is thrown.

[ne555]

> mutable Node *it;
¿why is that a member variable?

> listTemp = arg;
¿deep copy?

it->next->prev = it->prev;
it = it->next;
delete it->prev;

you are not deleting the node that you want, but the previous one (draw a diagram and you'll see it)

you need to make use of functions to simplify your code

for x in this.list:
   if other.list.is_member(x):
      this.list.erase(x)