https://www.youtube.com/watch?v=Yr82dyq7aT8 

SLS “Preview as Student” Error — What Happened and How to Fix It

While testing a Community Gallery module on SLS using Preview as Student, I noticed something strange — one activity consistently threw an error, while other activities loaded perfectly fine. Even more confusing, the problematic page worked normally in teacher mode.

Here’s a breakdown of what happened, why it happens, and how to fix it.

The Issue

The module and section loaded properly, but:

Problem Activity (fails):
https://vle.learning.moe.edu.sg/community-gallery/module/preview/36457328-4de5-4d80-8b84-576c25f0ee4e/section/54380723/activity/12116557

In Student Preview, this activity produced the following message:

“Something went wrong while performing this action. Please try again later.”

Working Activity (similar page):
https://vle.learning.moe.edu.sg/community-gallery/module/preview/36457328-4de5-4d80-8b84-576c25f0ee4e/section/54380723/activity/12116560

This one loaded perfectly in Student Preview mode.

Interestingly, both activities worked fine in Teacher/Admin preview mode.

What’s Causing This?

After reloading and inspecting the behaviour, a few consistent observations emerged:

Key Observations

• The error appears immediately on load

• Only Student Preview is affected

• Teacher/Admin previews are unaffected

• A duplicated copy of the same activity loads fine

• Both activities have identical content

Likely Root Cause

The evidence points to corrupted or orphaned student session data attached to the original activity.

When SLS runs a Student Preview, it attempts to initialize a simulated “student attempt.” If there’s corrupted or half-created data linked to that activity, the preview fails and shows a generic error instead of loading the content.

Why Only in the Community Gallery?

Community Gallery items don’t belong to actual classes, so preview data can come from:

• prior internal author testing

• auto-generated preview attempts

• old preview data that wasn’t cleaned up

• database inconsistencies

Since the duplicated activity worked, it strongly suggests the original activity had invalid student attempt data stored in the backend.

Fixing the Problem

Fortunately, the fix is very straightforward:

Solution

1. Duplicate the problematic activity

2. Delete the original corrupted activity

The duplicated activity has:

• fresh internal IDs

• no student preview data attached

• identical content

After doing this, Student Preview worked immediately with no errors.

If You Need to Report It

Because this involves backend session data, teachers don’t currently have the ability to clear it manually.

You can report it to the SLS helpdesk if needed:

• Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

• Phone: 6702 6513

Include the activity ID and specify that it only fails in Student Preview mode.

Final Thoughts

This behaviour highlights how useful (and realistic) Student Preview is — SLS tries to simulate real student attempts, which also means corrupted preview data can block loading.

In short:

• Symptom: Student Preview fails

• Cause: corrupted student session data

• Fix: duplicate and delete the original activity

For Community Gallery modules, duplicating is currently the cleanest workaround since there’s no teacher-facing way to reset student preview data.

If you’re testing modules and encounter mysterious Student Preview errors, this is a good place to start.

PS: this post supplement missing info site