If that occurs whenever you are using a .bmp image file, try changing the size of the actual image file itself so that it takes up more the screen. I like to use a free program called IrfanView. You can download it here: http://www.irfanview.com.

Once in IrfanView, open your image file. Then select Image > Resize>Resample. Pick a larger image size (maybe the same size as your monitor's screen resolution so that the image takes up the whole screen) and save the new image. Then try running it in DirectRT.

If it's not an image file that you showed in the uploaded screen capture, what kind of stimulus are running in the stim cell of you .csv input file that looks like that (i.e., text, video)?