Access Violations occured in the same place

I am using tidyparser to parse homepages of thousands of websites. There
always (about 1 of each 100 sites) occurred the "Access Violation" error
in the following code in ParseDefList function(at the last but 2 line),
what happened in it?

        /* center in a dt or a dl breaks the dl list in two */

        if (node->tag == tag_center)

        {

            if (list->content)

                InsertNodeAfterElement(list, node);

            else /* trim empty dl list */

            {

                InsertNodeBeforeElement(list, node);

                DiscardElement(list);

            }

 

            /* and parse contents of center */

            ParseTag(lexer, node, mode);

 

            /* now create a new dl element */

            list = InferredTag(lexer, "dl");

            InsertNodeAfterElement(node, list);

            continue;

        }