Database connection error

Annoyingly we have moved a site from our development server to our live server - we have edited the config file to allow the live site to connect to the database and have imported the database sql However, when we view the live site we see the annoying message "sorry cannot connect to the database" when we try to use the form on the site. Just need someone to look at the development site, and the live site and "make it work"! Obviously something really simple that we've missed. We have listed this project as xxx because we are aware that some providers will not appreciate the nature of the site - please note that there is no explicit content on the site at all.