If the error persists with an empty drum, clean the optical sensors:
Visually inspect the surface. If a master stencil is wrapped around it, manually open the clamp plate and gently peel the master away. riso error a16-525
If you have more details about the machine model or additional context about when the error occurs (e.g., during a specific operation), I might be able to provide more targeted advice. If the error persists with an empty drum,
Demystifying the RISO Error A16-525: Causes, Fixes, and Prevention during a specific operation)