If you are really using CS6(8.0) and not the update 8.0.2, that could be the problem.
In addition to what Larry said, I think you should contact Blurb tech support if you haven't already.
Most of us don't use that plug-in and can't be of much help.
- If the update doesn't fix it. Try Blurb Customer support: Book making help | Blurb (in gray in the lower right corner on this page).
- Also, you may want to un-install and re-install InDesign, maybe it lost the location for your User Dictionary?
Yes I was really using CS6 version 8.0. The problem also persisted in version 8.1.
Thanks for your suggestions. Blurb Support was the second thing I tried (after Google and InDesign support). The dictionary was indeed the problem. The 'English: Australian' dictionary appears to have disappeared and once I updated all my Paragraph Styles to 'English: UK' the problem seemed to resolve. Weird.
If anyone else experiences the same issue, here's the fix (thanks to Grabzoo on a previous discussion forum):
Open the Paragraph Styles panel and double-click any of the styles (i.e. [basic paragraph]). Click the 'Advanced Character Formats' tab on the left navigation menu; verify that Language is set to your preferred language (e.g. English: USA).
Do this for all listed styles, then save your document. Run spell check again and your problem should be solved.
This worked for me.
Thanks again for all your suggestions.