Hi Antonio!
Did reading blocks of 200 characters fix your problem ?
I have just the same problem as you. The application works fine when run at PC, but when downloaded to emulator or Pocket PC the app. crashes. I've tries reading in smaller blocks, but it does not fix my problem. With file sizes less than 1kB bytes (I've not found the exact limit) it works fine, but with files greater than 1kB the app. crash. No error messages are shown. (I've not attatched my source files, they are basically the same as yours)
If you have found a soulution to this problem please let me known.
Regards
Lars Erik