Hello Anass,
Thanks for the inquiry. You should make certain that the log path has the set permissions for at least read, write, and modify. I normally suggest to make certain the Network Service account has Full control over the directory path of the logs.
You should have the SmarterStats application running through IIS and the Application pool set to the Network Service as well. Make certain the Network Service account has full control over the SmarterStats folder as well.
If you have continued difficulties please consider opening a Support ticket so we may review the configurations.
Thanks.