Unable to add media into a media placeholder in MOGRTs

Hi there,

I am apparently unable to add media to a media placeholder in the properties panel of a MOGRT. When I drag and hold the media over the placeholder, the hand shows a stop sign underneath, as if this is not how I'm meant to add it. How am i meant to add media? I am experiencing no lag or crashes so I am wondering if there is something glaringly obvious that I am missing. Any help or advice would be greatly appreciated.