There is a system folder on the opus. Definitively. I see it with linux.
Did you contact bookeen ? Rather than messing up, you should contact them. If there is a
safe way to do that, they can point out what that way is.
Note that the first post referred to the mobi firmware, rather than the ePub one.
As to the book you've bought, don't you have a backup ?
Just out out of curiosity, there is library in Denmark that lend e-books ?