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This is to inform you that all HP Business Notebooks such as ZBooks, Probooks or Elitebooks have more stringent security than consumer models infact they don't produce 'halt codes', the password cannot be derived from the Serial Number and the code is stored in non-volatile memory so removing the RTC cell will not reset the password in this case.
Please Contact HP Business Notebook support they should be able to send you a customized SMC.bin file which you can use at boot to reset the password.
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K N R K
Although I am an HP employee, I am speaking for myself and not for HP