Plotbase would have printed those files, it's just that they didn't end in a an extension it recognized. I've gotten that error before, but still beeen able to add the files in Plotbase (ingnoring the error) and plot them successfully.
In my case, the customer was printing to disk with the win driver from an application that named the files *.PRN. Which isn't a supported extension, but the files came out fine anyway.
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