>>45
Grammatically correct, but makes no sense.
"That book is difficult to read while sleeping." makes more sense, but is still silly.
"That book is difficult to read while walking." would make sense.
But it doesn't have the original meaning anymore, whatever it was.
maybe the meaning was "That book is exciting." or "That book gave me nightmares."
Thing is that you cannot "sleep something". The only transitive sense (i.e. when the verb has a direct object) is when you "sleep with someone" (i.e. have sexual relations with that someone). You cannot, however, "sleep a book" - which is what is being formulated in >>44.
I suppose one could go to sleep with a book, so to speak, when one reads it before going to sleep and then falling asleep while reading it. That's still not expressed in >>44 either, though.
Maybe what was meant to be said was: "It's difficult to go to sleep when reading that book", meaning that going to sleep is a difficult task when you are busy reading the book.