Hi Edward,
Is it only the display of your desktop that rolls? If so, the solution is probably to set your desktop to the same format as the video that you use in applications such as Premiere Pro or After Effects. Please see Page 11 of the DeckLink Manual which is included as a PDF file in the latest drivers. Does that help?
If not, please provide a few details of the video format you are working with, the make and model of your monitor and also whether you are using genlock or trisync and to which video format it is set.
Regards,
Luke Maslen
Blackmagic Design