Uploaded folders are not being recognized by the task

Description of the problem:

My online task uses photos as stimuli, and the selection of photos differs by participant. I have a folder assigned to each participant by their ID number and within that folder is the CSV trial sheet, which contains the image file paths along with other stimuli, as well as a folder containing all of the photos. The CSV and the subject images all start with the participant’s ID, so because everyone has the same directory tree, it is written into the task to navigate to their folder using their ID using some string handling. I have been running this task for quite some time with little to no issues. However, with this recent batch of participants, three people have encountered the following error:

Unfortunately we encountered the following error:

  • when setting up a preload queue
  • unable to download resource: Participant_Images/[THEIR_ID_NUMBER]/[THEIR_ID_NUMBER]_trials.csv (Participant_Images/[THEIR_ID_NUMBER]/[THEIR_ID_NUMBER]_trials.csv)

Try to run the experiment again. If the error persists, contact the experiment designer.

This is especially odd because the path that is described in the error message exists, all of the folders are very much in the right place, no other study resources are missing, and nothing is misspelled. These are the only 3 in a batch of 15 participants that are encountering this error. When we pilot the task under any other IDs, the task runs as expected.

Any ideas on what could be causing this?

Thank you so much in advance.