Click on Publish.
I'm guessing that you meant that the Table of Contents is NOT well done. The Table of Contents is generated by assigning Heading Style 1 to the title of your book and to the title of the chapters. Don't try to insert a TOC. There are no pages in an ebook so a TOC listing the start page of each chapter is somewhat redundant.
If this is what is causing you the problem, strip out your TOC, assign Heading Style 1 as advised and then delete the old file and resubmit your Word document so that it is correctly converted to epub.
I'm having the same problem. No matter how many times, I revise following the instructions, delete and submit I still get the same error message :
HELP!!!! I'm stressed on this!