94 Invalid use of null

[edited from support email]

I am receiving an error message that says "94 Invalid use of null"
when I attempt to start one of my medialab experiments. I have
several other experiments that run properly on Medialab. I cannot
figure out what is causing this error message to occur, can you help?

Check all the questionnaire files for a blank item, or an item with missing
parentheses on the parameter values. If you can't identify the problem,
please send us the que files we'll take a look at them.