So far, it has frozen every time we try to run the full experiment (running the individual questionnaires, all are fine).

Because the questionnaires are presented in random order, it stops on different items each time --usually a Scale Response item, because those are the most commonly used -- but it is consistently at about item 145-155. If it has to do with the number of items written into the data files, then it is about item 160-170 (i.e., including time stamps, instructions, "ok" statements, etc.).

Once frozen, neither ctrl+right or ctrl+alt+right works; the only escape we've found (so far) is ctrl+alt+delete to get the Task Manager.