i'm glad you figured it out ! my next tip would have been to check the settings were not modified for impserve, and the tip after that would be "ask nick".
anyway now you know. i've never bought an .imp book myself, however i had some trouble at first getting stuff converted and transferred (it *is* complicated, sheesh !) and i used the auto online conversion service on filament books. i still do that from time to time, if i'm feeling really lazy.

it's a bit annoying that (as far as i can tell) there's no way to access your bookshelf through a browser, but that would be too easy, right ?