@milesahead:
Sounds like a DRM problem to me.
I'm sure there is software that is able to strip DRM from books, so a tool like Calibre can convert it to a different format that make it easy to read in your favorite reading software on your computer. Whatever this may be.
You are not allowed to use such software, and you probably shouldn't. Still, there is also something to say that you should be able to read your book on whatever device you own after purchasing that book. And as long as that book never "leaves" your library, the author/publisher/distributor aren't really hurting on the financial end. No harm, no foul.
-Shades
DeDRM Tools is a set of plug-ins for Calibre that will remove DRM from most purchased (but not rented or borrowed) Kindle/Nook/Kobo/Adobe ebooks. I use it for many ebooks I buy from Amazon, Adobe or B&N in order to read them in programs that handle footnotes and cross-references better than Kindle or Adobe Reader, or when I just want to keep an archival copy. Note that for Kindle ebooks, you will usually need to have available an older version of the Kindle reader for PC or Mac, or a very old Kindle device, in order to download a file in a format from which the DRM can be removed. That usually means a second PC or device.
DeDRM seems to have recently been forked and has a new developer who goes by the name noDRM. This lengthy
mobileread thread follows its development.