Dear Kamel,
in order to find out what is wrong, would you mind sending us the crash reports that the iOS creates automatically whenever an app crashes? This is how you find them:
When you synchronize with iTunes, the logs are transferred to your computer. Here are their locations:
• Mac OS X :~/Library/Logs/CrashReporter/MobileDevice/
• Windows XP: C:\Documents and Settings\\Application Data\Apple computer\Logs\CrashReporter/
• Windows Vista: C:\Users\\AppData\Roaming\Apple computer\Logs\CrashReporter/MobileDevice/
The log file names start with Notebooks and have the extension “crash”. They are just plain text files and can be sent by e-mail in original or zipped form, or even copy-pasted into your e-mail program. Please send them to notebooksapp@me.com
Thank you!