Something is definitely out of whack in that client-provided artwork. Probably some object with multiple instances of an odd effect or blending mode applied. Another thing I often see with PDF-based art files from clients is lots of duplicate objects stacked on top of each other. Astute Graphics' suite of plug-ins isn't cheap, but that Vector First Aid plug-in can sure save a lot of time and take care of various headaches. It doesn't solve every problem, but it takes care of a bunch.
ikarasu said:
But the best bet is to export it as PNG and move on!
I would only export and print vector artwork as a PNG or TIFF as a last resort. A good quality RIP, one that includes an Adobe certified PDF engine, should be able to handle any
properly prepared Illustrator-based artwork loaded into it.
The aggravating thing is so many self-taught clients preparing their own DIY artwork manage to come up with new ways how to do graphics work wrong. It can be baffling to dive into a layer's object tree to see the nonsensical ways some users will build up a piece of artwork. Adobe Illustrator is very prone to user mis-use. The same old usual motivations drive that madness, chiefly laziness. The amateur artist doesn't actually want to learn how to use an application properly, and he doesn't want to learn how he should prepare his art files properly for output. It's just easier to wing it. They're not worried about how the people who work in actual graphics production environments have to work with the garbage art files.
So, yeah, in the end rasterizing the artwork as a PNG or TIFF and printing that is about all you can do sometimes.