I have the same problem.
It's when you try to create an svg with several materials within it. For example, you load the can 1 preset into the curve editor of the lathe tool and save out an svg. You can then open in illustrator and export the svg without editing any elements in the file and try to load back into the curve editor, you will receive the same error. If you combine all into one shape, its OK. However, this isn't acceptable if you want to retain the can top, can bottom and can label materials. I hope this makes sense.
I'm using CC 2019 but I've also tried in CS6 and the same occurs.
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