I have run into this several times in the last couple of months. Today I did a render, saved it, then hide some objects in the view and then tried to render it again and got the following error message. I saved and reopened Rhino and it works fine.
James
Rhino Version 5 SR12 64-bit
(5.12.50810.13095, 10/08/2015)
Flamigo NXT
V3.1.2013.613