For security reason (as suggested by Better WP Security plugin), I changed the default wp-content name.
I can install this Count per Day but can't activate it. It said:
Warning: include_once(/home/mysite/public_html/wp-content/plugins/count-per-day/counter-core.php) [function.include-once]: failed to open stream: No such file or directory in /home/mysite/public_html/mycontent/plugins/count-per-day/counter.php on line 16
I managed to make it work by manually creating a folder named 'wp-content' at the root directory and copying the count-per-day's files (and its sub folders) to the folder.
Now it's working but I know it's not the best thing to do. Hope the next release of this plugin fix this issue. I found this information, hope it helps: