Thanks for the info -- this looks to be caused by the Box client on the computer in all likelihood. The Box sync process might have a lock on the original file, meaning Inquisit cannot add any data to it or makes some other change to the file (e.g. changing or adding some bits in the original to indicate its sync status) that causes Inquisit to no longer recognize and be able to write to that file.
It's probably the latter. You can simulate this manually by doing something like the following:
(1) Have Inquisit create a data file with the data for a bunch of runs. You'll end up with something that looks like this:
You see that the data from multiple runs was properly appended to the data file. Now,
(2) Open the file in e.g. Notepad and add some info to it that breaks its format, e.g.
Save and close the file. Then,
(3) Conduct another run with Inquisit. You'll see the same error thrown and a fresh file created: