Which of the two images in a trial do not appear? Is it consistent or random?

Have you tried different screen resolutions on your monitor or in the styles.drt file used with your .csv file? See this section of the DirectRT manual for information about the screen size option in the styles.drt file:

http://www.empirisoft.com/directrt/h...creen_size.htm

Also, are your .bmp image files 8 bit depth? You can check them by right clicking on the file, selecting Properties, and looking for the information in the Details tab.

Finally, make sure that your image file names are typed correctly in the .csv file and match the file names in the Stim folder exactly.