oh crap! I've fix the error! lolz! if anyone might encounter this, follow these instructions:
you must change the file permission (CHMOD).
How to CHMOD (change permissions) of some file ?
The easiest way to chmod files (change permissions) is using FTP client. Log on to your FTP account and select all files/directories you want to change permissions for. Right-click selected files and select File Attributes (in Filezilla) or Properties (in most of other FTP clients) menu. You will see some numbers like 644 or 755 (for example) in file attributes window. Change these numbers to any value you need (777, for example) and click OK button to confirm changes.
You can also change file permissions by using File Manager which is located on your cPanel.