Error after saving products

Have had a crazy weeknd with various OC problems. My site is now accessible again but a new problem.

I have an error on updating products which I have not seen before

2015-11-15 16:20:41 - PHP Warning: mysql_real_escape_string(): Access denied for user 'USERNAME'@'localhost' (using password: NO) in /home/MYSITE/public_html/vqmod/vqcache/vq2-admin_model_catalog_product.php on line 617
2015-11-15 16:20:41 - PHP Warning: mysql_real_escape_string(): A link to the server could not be established in /home/MYSITE/public_html/vqmod/vqcache/vq2-admin_model_catalog_product.php on line 617Access denied for user 'USERNAM'@'localhost' (using password: NO)

I have checked the config files and both have the username and passwords entered correctly

Site is Vers 1.5.4.1

Now that your host has updated your php and your site is using mysqli database driver, it looks like you may have a vqmod extension that is explicitly using a mysql function 'mysql_real_escape_string() rather than using $this->db->escape()