Thanks for this several suggestions and reply.

No, I am not it person  But I tried many thing and change nothing ...

I am sure that I must uninstall multibit and reinstall but I am scare to lost my money with this process ...

If I do :

- export key. My key will be save in my computer, right ?
- After I uninstall multibit
- After I reinstall  multibit
- and for finish, I import my key in multibit.

Like this, I don't lost something about my btc's, right ?

What I can get with this process ??