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Pavlovia Experiment - Stuck on loading


**URL of experiment: **
Operating System: Windows 10
Psychopy version: v3.03

Description of the problem:

I have designed a basic trial version of a change blindness flicker task that runs fine on my local Desktop. After uploading & activating on pavlovia to test functionality, the screen becomes stuck on loading the experiment.

In the console I am getting two errors:
“failed to load resource: the server /run/maxnni/csfp_v1[…] responded with a status of 404 ()”
“failed to load resource: the server /run/maxnni/csfp_v1[…] responded with a status of 404 ()”

[Image below]

All relevant files appear in the GitLab.

I am a first time user of both psychopy & pavlovia and have no prior knowledge of javascript & java, after browsing similiar issues on google / discourse I was unable to find any associated with psychopy.

Custom Code components are included in the study

Kind Regards,


Hi Max,

The issue seems to be around naming of the JS file and the experiment. It looks like the html file is referring to a file called:
MurphyFP_1.05 14.04.2019.js
but the appropriate JS file is actually called

I think this might be an issue with Experiment Name versus experiment file name that we’ve now fixed (along with various other improvements) so it would be worth trying with a newer version of PsychoPy (e.g. 3.0.7) regenerate your html code and try pushing back to pavlovia.

let us know if that doesn’t help


I just had a student with a similar issue–posting in case it helps anyone else. They updated to the most recent version of PsychoPy and re-synced to Pavlovia, but still was stuck on “loading the experiment…”

The original .psyexp filename (from Builder) had a space in it, so the corresponding .js files did, too. I thought that might be the issue, so the student renamed and re-synced. Still stuck. Then I found this post, and based on it, we went into the index.html file and found that the pointers to the .js files both started with “./” even though the .js files were in the same folder as index.html. We manually removed “./” and now it works just fine.

I’m not sure exactly where the folder-level discrepancy came from, but just in case someone has a similar issue, thought I’d post it!


Thanks for reporting, I had the same name issue, but manually changing it did not help.


I had the same loading issue. First, I changed the .js filenames in the Index file as suggested by @jeffbye above. However, it did not help. Then, in Chrome output, I noticed that I actually had a simple syntax error in my code element. I fixed it, and experiment started working. So, seems that different problems may lead to this “loading the experiment…” issue.


If you find a syntax error coming from the Builder-generated code ten let us know so we can look fix it more generally. Similarly, if the files are including “./” in file paths unnecessarily then we’d like to know when/why that’s occurring.

Providing links to your experiments (when they’re broken) really helps us look at an actual broken example and find the fixes.



Thanks, @jon. I had another student with a similar issue as well. I will ask them for their permission to share links with you (presumably by direct message if possible).


I don’t know if this will add any context but I recently updated from Psychopy 3.0.7 to 3.1.0 and I now get this error; but only after I moved the experiment file to a fresh new folder (i.e. the same experiment file works in the folder where the files were created in 3.0.7 (or older actually) but not in a folder where the requisite files were created in psychopy 3.1.0).

I should note that the experiment that successfully loads still doesn’t work but that’s due to a separate issue involving variable positions.

Loading error experiment -

Copy that’s ‘working’ -


Hi @JackB, I cannot see any JS files when I attempt to load your experiment. This used to happen when users changed the name of their experiment name (in experiment settings) so that it did not match their filename of the psyexp Builder file. However, this was fixed. Would you mind sharing your repo so I can see what is happening?


Hi @dvbridges, sorry I’m not sure what you mean by repo (repository? - the .gitignore file?), I’m fairly new to this program. I am though, happy to share whatever files will help.

I should mention that all my written code (which is relatively little) is in in python as I haven’t been able to convert it to JS yet.


Apologies! I mean your Pavlovia project repository that contains your files for your experiment. If I can see this, I can get an idea of what you have done, and why you are receiving these errors.


Ah I see, unfortunately when I try to access Pavlovia I get the ‘Error when fetching the experiments’ message; and upon attempting to re-login I get the ‘Error 500’ message, so I can’t link anything from the Pavlovia server. Perhaps they are all related as I haven’t had any of these issues before?

If there are any offline files I have which may be of use to you which I can upload, please let me know.


Thanlks @JackB, there was work taking place on the server, but should be up and running now.


Ok thanks for the update @dvbridges , I can safely login in now. I wasn’t completely sure how to do this, so I’ve invited you (or whom I assume to be you - ‘dvbridges’) as a guest on Github.pavlovia. If there is an alternative way that is easier or you require higher access just let me know. Please ignore the commit names, I was debugging lots of small things.

Writing this I’ve realised my experiment isn’t set to public, I can do this temporarily if it’ll help.

Lastly, my other experiment which was working is now stuck on loading experiment, and the only things that have changed is the ‘lastrun’ python file and the ‘data’ folder from offline testing. If you need access to this one just let me know.