This error usually prevents the action from completing and may sometimes cause the application to become unstable or crash.
Most occurrences of this error stem from older templates using obsolete expression properties or "pseudo-effects". When the JavaScript engine reads these deprecated lines, it throws an exception because the property data type no longer exists natively in the modern architecture. Run the Native Update Script
You have an expression (the little pick-whip code) linking one property to another. Sometimes, if the source property is deleted or renamed, the expression tries to "create" a link to a property that no longer exists, confusing AE.
Opening a project that uses effects from plugins you don't have installed (e.g., Boris FX BCC, Red Giant Universe). Pseudo-Effects & Presets: This error usually prevents the action from completing
If the error explicitly references a missing effect or third-party plug-in framework (such as Red Giant or Boris FX Continuum), the data fields cannot map correctly.
In simple terms, After Effects is trying to read a piece of data (a property of an object, like a color, slider, or position) but doesn’t recognize the format it's being given.
If the project was created in a much older version of After Effects, the expressions might need a syntax update. Run the Native Update Script You have an
: In rare cases, "Unknown Exception" errors are caused by missing or corrupt fonts that the script is trying to load for its UI.
: Upon opening, the system would scan for all custom pseudo-effects and prompt a download/link for missing ones.
After Effects Error: Asked to Create Unknown Property of Type [FIX] Pseudo-Effects & Presets: If the error explicitly references
If you are working with a Motion Graphics template (.mogrt) from Envato or Adobe Stock:
Sometimes, After Effects tries to read from a corrupted cache file, leading to "Unknown Property" errors during preview or render. The Process Navigate to Edit > Purge > All Memory & Disk Cache. Click OK to confirm. Restart After Effects and try opening the project again. Step 4: Reset After Effects Preferences