Unwanted/unprogrammed blank/black screen and button press? (case 16706)

[hou1b]

I've programmed my stimuli to appear and disappear as planned but when I ran the .csv file, from time to time a blank/black screen would show up, and it wouldn't go away unless I pressed the space bar. In my programming, I do have a black image (that creates the visual effect of a complete blank screen since the background for all other image stimuli is black) in a stimuli list .txt file among other images, and if it works properly, the black image will be randomly presented and will disappear automatically in 1500 ms. All other images I programmed in my study appear and disappear on cue... I can't figure out why the blank screen doesn't. Any help would be highly appreciated.

Thanks in advance!