How to Fix “InvalidOperationException: You are trying to read Input using the old input system” in Unity

This exception appears the moment you install the Input System package and restart: every legacy Input call now throws. You choose a lane — migrate, or run both during the transition. Here is how.

How to fix it

1. Pick the transition mode deliberately

Project Settings > Player > Active Input Handling: 'Input System Package' hard-breaks legacy calls; 'Both' lets old and new coexist while you migrate incrementally.

2. Migrate the hot paths

Replace Input.GetAxis("Horizontal") with an InputAction from an action asset, and UI's Standalone Input Module with the Input System UI module on the EventSystem.

3. Fix the assets you did not write

Store assets and old samples poll the legacy manager; check for updated versions or wrap them until replaced — the stack trace names the calling script.

4. Finish the migration before shipping

'Both' costs a little per-frame overhead and hides stragglers. Grep for UnityEngine.Input. once migration feels done and switch to the package-only mode.

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 Unity 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.