This document's page tree contains an invalid node

We have some PDFs that our users add pages and bookmarks to from time to time.

In one of them, once we go to bookmark no. 61 I receive the error message "This document's page tree contains an invalid node."  I receive that same message for every bookmark after No. 61

I can delete the bookmarks but still can't access the pages.  If I try to navigate by paging down through the PDF only a small thumbnail of those pages displays.

When I try to delete the affected pages, I receive the error message, "Expected a dict object"

I've tried extracting only the pages above where the "problem bookmarks" begin.  Unfortunately, I receive the error "this document's page tree contains an invalid node" when I try to do so.

Any ideas how I can resolve this issue?  I appreciate any help or ideas on this matter.

Thanks.