Warning: session_start()

I have had no problems with my opencart website until today when I visited the website and found this error at the top of the page:

Warning: session_start(): open(/tmp/sess_4883dj6e137vhik2hiju3lbpl4, O_RDWR) failed: Permission denied (13) in /home/sites/funblueplaques.com/public_html/system/library/session.php on line 11

I found a solution which removed the error, however I have another issue where I can't login to the admin panel with or without this session fix.

I enter my admin login details and then I click login and it just refreshes the page and won't let me login.

Any ideas?

Here is the website: http://217.199.187.63/funblueplaques.com/

set your session files to another directory if you do not have permission for it, else contact your web host to solve it for you.