How to Fix "An error has occurred" when using Undo in 3ds Max

When pressing Ctrl+Z (Undo) in 3ds Max triggers an "Application Error" crash, the cause is almost always an infection by a malicious third-party MAXScript known as ALC. This script silently corrupts 3ds Max settings and scene data, making basic operations like Undo unstable or impossible.

ALC is not a traditional virus — it is a MAXScript that spreads through infected .max scene files. When you open an infected file, the script installs itself into your 3ds Max startup directory and then embeds itself into every scene you save afterward. This makes it particularly dangerous in collaborative environments where artists share scene files.

How ALC Infects Your System

The infection process works in two stages:

Stage 1 — Scene Infection: You receive a .max file from a colleague, client, or asset library. Unknown to you, the file contains an embedded ALC script. When 3ds Max opens the file, the script executes automatically and copies itself to your 3ds Max startup scripts directory.

Stage 2 — System Infection: Once in the startup directory, the ALC script runs every time 3ds Max launches. It then embeds itself into every scene file you save, spreading the infection to anyone who opens your files. It also modifies 3ds Max's internal script controllers, which is what causes the Undo crash.

The script is designed to be invisible — it does not display any obvious symptoms initially. Over time, it corrupts script controller data, breaks the Undo stack, causes intermittent crashes, and may affect render output.

Symptoms

ALC infection manifests through several symptoms, not all of which appear immediately:

• Undo crashes 3ds Max with an "Application Error" dialog
• Script Controller errors appear unexpectedly ("No 'Get' function for undefined")
• Scenes become progressively unstable — operations that worked yesterday crash today
• File sizes increase as ALC data accumulates
• Other artists report problems after opening files you have saved — this is the infection spreading

Detection

Check Startup Scripts

Navigate to your 3ds Max startup scripts folder: C:\Users\[username]\AppData\Local\Autodesk\3dsMax\[version]\ENU\scripts\startup\

Look for unfamiliar .ms or .mse files. ALC scripts often have generic names to avoid detection. If you find scripts you did not install, they may be ALC or similar malware.

Use Autodesk's Security Tools

Autodesk provides the 3ds Max Security Tools plugin specifically designed to detect and remove ALC and similar script infections. Download it from Autodesk's official website:

1. Install the Security Tools plugin
2. Open 3ds Max
3. The tool runs automatically and scans for known malicious scripts
4. Follow the prompts to quarantine or remove detected infections

This tool is the recommended first step and catches the majority of ALC variants.

Check the MAXScript Listener

Open MAXScript > MAXScript Listener (F11) and observe the output when 3ds Max starts. Suspicious entries include references to unfamiliar scripts executing at startup, or error messages about script controllers.

Cleanup Process

Step 1: Run Autodesk Security Tools

Install and run the Security Tools as described above. This handles the automated detection and removal of known ALC variants from both the application and open scene files.

Step 2: Clean the Startup Directory

Manually inspect the startup scripts folder and remove any unfamiliar .ms/.mse files. Compare with a clean 3ds Max installation if possible — the startup folder should contain only scripts you recognize (plugin initialization scripts, custom tools you installed).

Step 3: Reset 3ds Max Preferences

Hold Ctrl+Shift while launching 3ds Max to reset all preferences. ALC modifies preference data that can persist even after the script itself is removed. Resetting preferences ensures a clean state.

Step 4: Clean Infected Scene Files

Open each recent scene file with the Security Tools installed — the tool will detect and remove ALC data embedded in the scene. Save the cleaned file under a new name to preserve the original as evidence.

If the Security Tools cannot clean a severely corrupted scene:

1. Open the infected scene (with Security Tools active to prevent re-infection)
2. Select all geometry
3. Export as FBX
4. Create a new, clean scene
5. Import the FBX geometry
6. Rebuild materials and render settings

This is destructive — you lose render settings and V-Ray/Corona materials — but it guarantees a clean scene file.

Step 5: Notify Your Team

If you shared any scene files after the infection date, notify everyone who received them. They need to run the same cleanup process to prevent the infection from re-entering your pipeline through their files.

Prevention

• Always run Autodesk Security Tools — keep it installed and active permanently
• Be cautious with external .max files from clients, freelancers, or asset marketplaces
• Scan scene files before opening when they come from untrusted sources
• Use FBX for asset exchange instead of .max files when possible — FBX cannot carry MAXScript infections
• Keep 3ds Max updated — Autodesk introduced script execution controls in 3ds Max 2021 and has continued to strengthen them in subsequent releases, including stricter prompts before running embedded scripts from untrusted sources

ALC infection can also cause general 3ds Max freezing and slow performance as the malicious script accumulates data over time.

Impact on Render Farm Submissions

ALC-infected scene files can cause problems on render farms too. The malicious script may execute on render nodes (depending on the farm's security configuration), potentially corrupting the node's 3ds Max installation or causing render failures.

On our render farm, we maintain security scanning on all incoming scene files. However, we recommend cleaning infected files before submission to ensure consistent render results.

FAQ

Q: What is ALC and how does it get into my 3ds Max? A: ALC is a malicious MAXScript that spreads through infected .max scene files. When you open an infected file, the script copies itself to your startup directory and embeds itself in every scene you save afterward. It is not a traditional virus — it operates entirely within 3ds Max's scripting environment. You can get infected by opening scene files from colleagues, clients, or asset marketplaces.

Q: Can ALC damage my renders or output files? A: ALC primarily corrupts scene data and script controllers, which can affect render output indirectly. Materials may not evaluate correctly, animations may behave unpredictably, and script-controlled parameters may produce wrong values. The Undo crash is the most visible symptom, but data corruption can affect any aspect of the scene.

Q: Is my entire machine infected, or just 3ds Max? A: Just 3ds Max. ALC operates within the MAXScript environment and does not affect your operating system, other applications, or files outside of 3ds Max scenes and settings. However, every .max file you save while infected contains the ALC script, so those files can spread the infection to other 3ds Max installations.

Q: How do I know if my scene files are clean after running Security Tools? A: After running Security Tools on a scene, re-open it and check the MAXScript Listener for any suspicious output. Test the Undo function with a simple operation (move an object, undo, redo). If Undo works without crashes and the Listener shows no unfamiliar script activity, the scene is clean. Save the cleaned scene under a new filename for safety.

Q: Are newer versions of 3ds Max immune to ALC infection? A: Not immune, but better protected. Starting with 3ds Max 2021, Autodesk introduced script execution controls that prompt the user before running embedded scripts from untrusted sources. 3ds Max 2025 and later versions further tighten these controls. However, if an artist clicks "Allow" when prompted, infection can still occur. Always keep the Security Tools plugin installed as an additional layer of protection.