This error usually pops up when After Effects is trying to interpret a script, expression, or pseudo-effect (a custom controller) that it does not recognize or that has become corrupted. As of 2026, this often relates to bridging older project files with the latest, highly optimized AE expression engine.

folder (located in your Adobe After Effects installation directory) and re-add them one by one to find the "troublemaker". Check Plugins

This can sometimes occur due to expressions or scripts trying to access properties that no longer exist or have been renamed. Review any expressions or scripts in your project.

General corruption can lead to "unknown BIB" or property errors.

: Faulty dockable script panels ( .jsx or .jsxbin files) firing background commands that the software's active architecture doesn't support. 5 Ways to Fix the "Unknown Property" Error 1. Update Legacy Expressions

Don't worry; we've got you covered. Here are some solutions to fix the "After Effects error asked to create unknown property of type" error:

C:\Program Files\Adobe\Adobe After Effects (version)\Support Files\Scripts\ScriptUI Panels

To check all expressions at once: Edit > Find → Search for toFixed( → Check the box .

If the error prevents you from opening your .aep file, you can often bypass the corrupted property check during startup by importing the file as footage. Launch and create a completely blank project.

: If the project was created on another machine, ensure all third-party plugins used in that project are installed on your current system. Import into a New Project

Opening a project that uses effects you don't have installed can trigger "Unexpected data type" or property creation errors. Step-by-Step Fixes 1. Identify and Remove Problematic Scripts