After Effects Error Asked To Create Unknown Property Of Type __top__ May 2026

"ADBE Mask" , "ADBE Effect" , "ADBE Paint" , etc. Wrong: passing a custom string that AE doesn't recognize.

try { myLayer.property("unknownProp").setValue(10); } catch (e) { alert("Property missing: " + e.message); } If you provide the that triggers the error, I can give a targeted fix. after effects error asked to create unknown property of type

Use PropertyGroup.addProperty() with a known match name or display name, or create via PropertyGroup.property("ADBE...") . 4. Expression trying to create properties dynamically Expressions cannot create new properties permanently. If you're trying to write a custom value into a non‑existent property, AE will throw this error. "ADBE Mask" , "ADBE Effect" , "ADBE Paint" , etc

if (layer.hasOwnProperty("sourceRectAtTime")) { // safe to use } When using ExtendScript ( app.project.item(1).layer(1).property.addProperty(...) ), you must use a valid property type string. Use PropertyGroup

Pre‑create the property via a script, or store custom data using text.sourceText on a hidden text layer or marker.comment . 5. Script expecting a specific AE version property Some properties (e.g., 3D Gizmo, Cinema 4D renderer options) exist only in newer versions.