Hi,
Since recently, Rhino 8 shows this error at startup:
Unable to load RhinoCycles.rhp plug-in: ID already in use.
The root cause seems to be Windows Smart App Control blocking RhinoCycles.rhp. Rhino itself is installed from the official McNeel download.
Note: my Windows is in Czech, so some screenshots are in Czech. Translations are below.
Screenshot 1 – Windows Security notification
Translation: “Part of this app has been blocked. Some features of Rhino 8 may not work because we can’t confirm who published RhinoCycles.rhp that the app is trying to load.”
Screenshot 2 – Rhino plug-in error (shown right after the block, probably just a consequence of it)
Screenshot 3 – Digital signature of RhinoCycles.rhp
The file is signed by McNeel Software Development, issued by “Trusted Rhino Plug-ins”, signed on 11 Aug 2026 with an SSL.com timestamp. Windows reports “The certificate in the signature cannot be verified” and “Windows does not have enough information to verify this certificate.” As far as I understand, the certificate chains to McNeel’s internal CA, which isn’t a trusted root in Windows. Smart App Control therefore treats the file as unsigned.
Screenshot 4 – Event Viewer, CodeIntegrity/Operational, Event ID 3077
Code Integrity determined that a process (\Program Files\Rhino 8\System\Rhino.exe) attempted to load \Program Files\Rhino 8\Plug-ins\RhinoCycles.rhp that did not meet the Enterprise signing level requirements or violated code integrity policy (Policy ID:{0283ac0f-fff1-49ae-ada1-8a933130cad6}).
The log also shows repeated 3033 / 3089 events every time Rhino starts.
System:
- Version 8 SR34
(8.34.26223.11001, 2026-08-11)
Commercial - Windows 11 Pro (Czech), Smart App Control On
FYI I saw .. topic Why Smart App Control has blocked part of this rhino8 app it looks it is the same issue.
Pls. Help 
Thank you.
Tomas.