Using Views PHP with external database data causes white screen of death

Hi,

I've currently got a view that allows Drupal to use an external database to display content from a table. Now I would like to add a Global: PHP field using the Views UI that would enable me to make calculations that I require. When I select the Global: PHP from the UI and echo out a basic message such as "hello world", I get a white screen of death until the field is removed.

From my understanding, this is because I'm using external data outside the Drupal database. I would like to know if there is any way i could possibly have access to using the Global: PHP field while using an external database within a view.

It would be worth mentioning that I've defined a database connection in settings.php and in order to get the external data to be displayed in the views, I've used hook_views_data() in a custom module.