آقای فیروزمندان درست می فرمایند.
توی بخش تیکت بلوهاست گشتم نوشته بود برای فعال کردن save session path باید php.ini واقع در روت اکانتت رو ادیت کنی
کد:
Open the File Manager 
Right click the php.ini file inside public_html. 
Select Code Edit 
Around line 824 is something which looks like this: 

;session.save_path = /tmp

Remove the semicolon ';' in the front so it looks like this: 
session.save_path = /tmp

Finally, make the path go to the temp folder on your account 
session.save_path = /home/username/tmp 

where username is your cPanel username listed inside of cPanel.

Save the Changes 
Additional Notes:

If the error persists, one of two things can be done:

Place a copy of the modified php.ini file into the "administrator" or other appropriate folder 
Inside cPanel, select the PHP Config icon, enable PHP 5 (FastCGI) and Save Changes