The CHM Reader takes a ridiculous amount of memory to run. If you have a book that doesn't read, free any and all memory you can. This is especially important if the book you read is more than just a few megs in size.
As far as I know every book I tried opens correctly in chm reader, as long as you have enough memory. I wish I had some time to improve it a bit, it's a very useful app.
--Eric
