Psykinematix

The experiment we need to conduct is a 2-AFC between two .avi files select from a pool of many. The stimuli are divided into two categories and there are about 500 each. The filename has coding for whether a particular element that the observer is looking for exists in the film clip or not. 1xxxx.avi does not have the element; 2xxxx.avi does have it. I need to record which stimuli were shown (though this could simply be the file order) and have the observer select between temporally ordered pairs. Since the file name has the 'answer' I thought using [SELECTION] as the variable would work. The 2-AFC does not need to adjust anything, just show the next pair of stimuli after the observer responds and the system gives feedback. Using [SELECTION], it displays the first pair of stimuli but then aborts. The log gives a warning, but not one specific enough for me to interpret.

Any ideas?