We've created this Forum Thread with some workarounds and advice to assist you in publishing you ebook.
Epub goes through just fine on Smashwords or Draft2Digital, but not Lulu. Hmmm
I often create documents using the Atlantis word processor, which has the capability to save directly to an Epub file. The files have been so good, in fact, that not only do they always pass with flying colors when I put them through here:
They ALSO pass without any issues when submit through Smashwords and Draft2Digital for retail distribution....and end up on Nook.com and iTunes without any problems.
But yet when I run them through Lulu it always says I have errors with the epubs. Then when I turn around and try the regular document as opposed to the epub it says it can't create the epub.