After Effects Error Asked To Create Unknown Property Of Type Fix Site

This error typically occurs when After Effects encounters a pseudo-effect (custom effect controls) or a Master Property

Change Expression Engine: If the error is expression-related, try switching engines. Go to File > Project Settings > Expressions and change the engine to Legacy ExtendScript. This error typically occurs when After Effects encounters

General corruption can lead to "unknown BIB" or property errors. Select all layers in your comp (Ctrl/Cmd + A)

However, I can offer some general troubleshooting steps and potential fixes that might help resolve or at least help you troubleshoot the issue: If you have the Essential Graphics panel open,

macOS: /Applications/Adobe After Effects (version)/Scripts/ScriptUI Panels

• Select all layers in your comp (Ctrl/Cmd + A).
• Hit EE on your keyboard (this reveals all expressions on selected layers).
• Look for any expression with a yellow warning triangle or one that references property("FIX"), fixValue, or strange numeric arrays.
• The fix: Delete the offending expression or rewrite it using standard JavaScript (e.g., instead of trying to force a FIX, use value[0] for a simple number).

• If you have the Essential Graphics panel open, close it before opening the project.
• If you can open the project, go to the Essential Graphics panel and click "Push Changes" or remove any properties listed there that might be broken.

If the error persists

Don’t worry. You don’t need to reinstall Windows or trash your entire project. Let’s break down what this means and how to get you back to animating.