Blank screen when presenting stimuli

Hello,
I am having an issue with the stimulus presentation for a study I am preparing to run. In the study, participants will make judgments of 40 different behaviors randomly selected from a total set of 120. For each behavior, participants make an initial judgment framed in one of two randomly determined ways (done using the sublist option new to version 6) followed by a second judgment of the behavior that is not randomized. To ensure consistency in presentation, all judgments are presented to the participants as image files and they give their response using the keypad. Each set of judgments is also preceded by a fixation cross and also includes an event marker sent to a biopac system (we intend to collect skin conductance data while the participants make their judgments).

Recently, we have been encountering an issue where, after presenting the judgment image files correctly for roughly 12 behaviors, superlab starts presenting a blank screen instead of the judgments that continues for the remainder of the study. The fixation cross continues to appear correctly and the event marker is showing up correctly in the biopac data. Similarly, superlab continues to log responses made using the key pad and which image should have been presented in the data file.

Any help you could provide with this issue would be greatly appreciated. I am also happy to provide the zip file of the experiment if it would be helpful in resolving this problem.
Thanks,
-Dan