Set up external dvd drive on iMac

Hi,

My superdrive started acting funny (not ejecting discs and then not reading them), so I bought an external dvd player/drive.
Everything worked fine until I installed an SSD in the place of the superdrive.
Now, when I go to play a DVD in the external drive DVD player says "There was an initialisation error, a valid dvd player was not found"

Other apps do not recognise the dvd either, as they used to.

Disk Utility will find the dvd if one is in the player but will not find the player if there is no DVD.

Is there something I can do to make the iMac recognise the DVD player as the player by default?

Thanks

iMac 24inch early 2009

El Capitan updated

Samsung SE208 portable DVD writer