With CRP set to CRP1 or higher, available boot sources are restricted: If the requested boot source (either hardwired boot source from OTP or read from pins) is not one of UART0/UART3, the boot code forces booting from UART0.
So there is no way to boot into USB DFU mode (as required by LPCScrypt) on a CRP protected device. You will have to unlock over the UART using Flashmagic or similar first.
Regards,
LPCXpresso Support