Hi Elise,
What 404 error exactly are you referring to? The experiment at the link you gave works quite well for me: the zip file gets downloaded (as visible in the Logs tab of the Debugger: [15:17:19] Download of https://chaipictures.s3.eu-central-1.amazonaws.com/Pictures.zip complete (PennController: 31)) and the resources get preloaded normally.
The Errors tab does report a few errors, but they have to do with your Template commands referencing tables named “Practice_N” (with N a number from 2 to 6) when the only tables you have in your experiment come from the files “Materials_fillers_Questions.csv,” “Materials_DO_Questions.csv,” “Materials_fillers_Pictures.csv,” “Materials.csv,” “Materials_DO_Pictures.csv”, and “Practice_1.csv” (the debugger suggests that you reference that file instead).
It’s true that I do get a 404 error in the web console for https://expt.pcibex.net/ibexexps/Potsdam-experiments/Chai/1.jpg, but that’s because PennController always also looks for each resource file locally (ie. at the experiment’s URL) even if you use a ZIP file (or the AddHost command) and then uses the first file that is successfully resolved by one of the requests (local, zip, distant host).
Best,
Jeremy