HTTP Error Code 500 Internal Server Error when trying to create Dynamic MySQLi connection

When I try to create a Dynamic MySQLi connection from Dreamweaver CS 5.5 to a remote MySQL database, the following error appears when I click the Select button in the Primary Connection tab...

HTTP Error Code 500 Internal Server Error

My website is setup to force https and the non www. version is used. This is reflected in Site Setup with the Web URL option being set to https://domainname.com. However, I have tried all combinations http/https/www./non www, along with turning off forcing https and non www.. No change works and all report error 500.

I was able to connect to the database without problem when using Dreamweaver's built in MySQL connector BEFORE I installed the Dynamic MySQLi extension. Now I can't even do that with it too throwing a 500 error. I CAN connect to the database remotely using Navicat though - using the same settings I have tried in Dreamweaver.

I have deleted the _mmServer Scripts folder, exited and re-launched Dreamweaver, recreated the cache. Nothing resolves the problem.

Hope someone can help please as I need to get this up and running.

If I can't get this working can someone send me the PHP code the extension creates for a login, checking a user name exists (for sign-up), a query, an insert, an update and a delete please. Just need get this working no matter the process.