We've created this Forum Thread with some workarounds and advice to assist you in publishing you ebook.
Unknown issue while trying to convert your file to an EPUB.
I tried to upload a technical book that contains 234 pages. The file contains custom styling such as various fonts for code examples). When I uploaded the docx document I got textbox error. I didn't use text boxes.
Then I copied a chunk of text and created a test.docx file. It validates in EPUB Validator (beta).
But I get an unknown error from Lulu wizard.
I have attached the document. If anyone can help to solve this issue, it would be great.