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.
AE relies heavily on the GPU for rendering. If a property relates to OpenGL or CUDA, outdated drivers can cause creation errors. after effects error asked to create unknown property of type
Faulty extension scripts running in the workspace often trigger automatic background property generation, causing a system mismatch.
Older animation presets often contain obsolete expression methods that the modern JavaScript rendering engine cannot decipher. asked to create unknown property of type | Community if (layer
If the error happens without a project open, it might be a script.
Pre‑create the property via a script, or store custom data using text.sourceText on a hidden text layer or marker.comment . Faulty extension scripts running in the workspace often
Wrap the offending line in a try...catch to at least prevent the error from stopping the whole script:
If the error happens on startup or random actions, a plugin is likely at fault.