The operation cannot complete because of an unknown error [NOKY]
melb shared this idea
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.