insert a node after an iter postion in a deque class

I'm having problem to insert a node right after an inter position, keep having the un-handled exception, even though I check all the links to the pointers and they are all correct. Would anyone take a look at my code and see what's going wrong please ?

void insert_after(DequeIterator<E>& iter, E x)
{
    if(_size == 0)
    {
        insert_front(x);
    }
    else
    {
        assert(!iter.at_end());

        // need to check, if its the iter is the last element
        // do insert_back instead
        if(iter.node() == _tail)
            insert_back(x);
        else
        {
            // create a temp2 pointer to hold the address of iter
            DNode<E>* temp2 = iter.node();
            // set temp2 equal to the address of the node after
            // iter before inserting
            iter.node()->next()->set_next(temp2);
            // create a new node to insert
            DNode<E>* temp = new DNode<E>(iter.node(), x, temp2);
            // set the iter->next to hold the address of the new node
            iter.node()->next()->set_next(temp);
            //set the address of temp2->prev to hold the address
            // of the new node.
            // This is also where I got the exception error !!!!
            temp2->prev()->set_prev(temp);
            _size++;
        }
    }   
}