Where are the books coming from? Are they downloads from Fictionwise (for example) or home-grown?
Books with an IMP extention are not readable across the various ETI readers, so it might be that you have the "wrong type" of IMP.
I'm a little rusty on this since I gave my old eBookwise to a co-worker a couple years ago, but if I remember correctly, when I downloaded multi-format books from Fictionwise for the eBookwise, I used the OEBFF Half-VGA. Since you say you have the other one, you might try the "Full VGA" version (this depends on how your got your ebooks, natch).
Last edited by FizzyWater; 07-29-2011 at 08:52 PM.
Reason: added information about Fictionwise formats