Clear Scren During RT with No Response as Valid

Hello,
What I'm trying to accomplish is to have a stimulus (letters) appear on the screen for 250ms, during that time and for a short time after(1000-4000ms) they are able to respond by pressing the spacebar. If an 'X' appears on the screen, they are not supposed to press anything.
I know that putting clear250 in the time column will cause the stimulus to disappear after 250ms. I also know that putting -1 in the time column makes no response valid. And in the .drt file I have set the MinMax values appropriately. However, when I run the file, the trial will not end until I respond, even when 'no response' is the correct response. I tried running it just without the clear250 and it worked, I also tried it just without the '-1' and it worked. Can DirectRT just not accept as many conditions as I have applied? Any help or ideas would be appreciated, thank you.
I have attached a copy of the experiment folder if it would help to see what I'm doing.