Take a look at the API table referenced in the message (Table 3-1). Notice that the table only goes as far as a bottom shell course thickness of 1.75 inches. You're exceeding that, hence the error message.
That sounds very strange, this shouldn't happen. If you have reviewed your input and still can't find the problem, open a Support Request on eCustomer and submit your job file for review.
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Regards,
Richard Ay - Consultant