The operation cannot complete because of an unknown error [NOKY]
The problem caused from the big large of dimension of the artboard because you would use the real dimensions of design, So scale the dimension of artboard in 1/10 for example and the problem will solve
Had this today. I opened the file in Acrobat, Saved as EPS and reopened in AI. Problem was resolved. This is just a workaround not a fix.