If you're reading this article it's because Blurb's customer support team has sent you here. Most likely you created a cover for your book or magazine and then changed your final page count, and saw an error message similar to this:
The number of pages in your book must be from XX to YY pages in order to be compatible with the spine width of the current cover template. If you need a book with a page count outside of the specified page range, please create a new book.
Why this happens
When you create your cover, the plug-in sets the cover dimensions based on your specific page count. If you later change your page count this can make your existing cover unusable. (That's why we recommend waiting to design your cover until you've got your final number of pages).
Don't worry though...you don't need to recreate your entire book. You will, however, need to follow these steps in order to pair your existing pages with a correctly-sized cover. In short, you'll re-use your existing pages file, and possibly your existing cover file, to create a new book.
What you need to do
1. Use the Book Creator plug-in to set up a new publication with the same book size, paper type, cover type and ISBN option as the original...but with the updated number of pages. (This is the info you see in Step 2: Book Details as seen in the screenshot below).
And don't worry--you won't need to recreate the publication from scratch...this step just sets up the correct specifications.
2. Now locate your pages file: in Step 3: Document Files don't click Create Pages file. Instead, click the link icon as seen here and then locate/click on your original InDesign pages file.
3. Now click the edit button (the pencil icon) for the pages file to review your file and ensure everything looks the way you want it to. You can make any desired changes to the pages at this point.
4. Once you're done reviewing the pages, and certain that you won't add or remove pages again, you can do either of the following. (Both methods will let you create a cover with specifications that now match your page count).
a. In the Step 3: Document Files section click "Create cover template" and create a new cover from scratch.
Or
b. Click the link icon for the cover then choose the "Resize and Link" option. You'll see a message reminding you to review the newly resized cover file since content may shift.
The cover options
The Resize and Link option if linking to the existing cover file.
5. When ready to upload, click the blue "Upload book" button in the Book Creator interface. Be sure to review the exported PDF carefully, before continuing with the upload.