Can't drag & drop to Rasterlink 6

Hi everyone,
Please help with this very frusterating issue.
We bought a new Mimaki (also have roland and Versaworks RIP, no problems there...) and we print hundreds of different files a day.
For some reason the software just won't allow me to drag and frop my PDF files! In order for me to print them, I need to use File -> Open, which is very time consuming when talking about hundreds of files.

Anyone has any idea why I can't drag & drop?

Thanks in advance :)