How to Fix “Unable to find instance for object index” in GameMaker

An instance-not-found error means you used an instance that is gone or invalid. Validating it fixes the crash. Here is how.

How to fix it

1. Check instance_exists

Before using a stored instance id, call instance_exists. An instance you destroyed, or one that never spawned, no longer exists, and using it errors. The check turns that into a handled case.

2. Validate stored ids

If you save an instance id to use later, the instance may be destroyed by then. Re-validate it before use rather than assuming it still exists, especially across rooms or over time.

3. Distinguish object from instance

Using an object index where an instance id is required (or vice versa) causes confusion and errors. Be clear which you are passing — object for type checks, instance id for a specific object.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every GameMaker error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.