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