For MySql you need to download our data layer for mysql from the codeplex download page and replace the dlls in the /bin folder with the ones from there(MySql connector is included in the package you don't need to download it separately). See the article Using MySql.
You need to make sure that .NET framework 4 or ideally 4.5 is installed and enabled on the site in IIS.
Then if you still get errors see Basic Troubleshooting
Note that if user.config exists in the root of the site then that is where to set the connection string.
Other articles that may help you: Manual Installation Recipe for IIS 7.x