We've created this Forum Thread with some workarounds and advice to assist you in publishing you ebook.
Assigning an ISBN to an existing project
It is possible, once you've completed publication of your book, to add an ISBN and begin the distribution process. The first step is to create a revision of your project.
To do this go to My Projects and click the Revise link next to the project you want to edit. This opens the details page for that project. Click the "Create New Revision" button at the top of this page to open the publishing wizard.
In the "Options" step you can confirm your book's size, paper type, binding, etc. Not all book sizes and formats qualify for distribution. Distribution-eligible book formats are designated by a green check (tick) mark. These are the formats that can be assigned an ISBN.
Learn more about distribution eligible formats.Once you have selected and/or confirmed your book's format options, click "Save and Continue."
In the Title step, choose the option to "Sell on Lulu, Amazon, Barnes & Noble, and More."
This will generate the ISBN step in the publishing wizard. Once selected, click "Save and Continue."
The ISBN step in the wizard provides two ISBN options. You can select "Get a free ISBN from Lulu.com" or "Add an ISBN you already own". Make sure to read the ISBN agreement posted next to your choice for additional details. Once complete, scroll down and click "Save and Continue." The next page is an ISBN confirmation page that includes a PDF image of your ISBN barcode. You have now officially added an ISBN to your book! Click "Save and Continue."
In the Cover step, your ISBN barcode will automatically be added to your book cover if you use the cover design wizard. If you have created a one-piece cover, you will need to add the ISBN barcode image to the cover before you upload it.
Proceed through the remaining steps, saving as you go and checking to make sure everything looks accurate. Continue through the wizard until you reach the Review stage. Carefully verify all details of your revision at this point and download the print-ready files by clicking on the white page icon with the green arrow next to the file names to review them. Once you are satisfied that everything is in order, click on Save & Continue until you get to the "Congratulations" screen.
To place your book into distribution, click the purple "Manage" distribution icon next to your project's listing.
Please note: You must purchase and approve a proof copy of your project before submitting it into retail distribution.