Hi Shaun,
I already get the reply from our according department.
They also have reproduced this problem in IAR project, they will try to fix it in the near future, so please wait patiently.
Now, we have test the LPCXpresso project, that usbd_rom_cdc_uart project works well with LPCXpresso IDE.
So do you mind to use the LPCXpresso project now?
You can download and install the LPCXpresso IDE at first, then import the lpc_board_keil_mcb_1857, lpc_chip_18xx and usbd_rom_cdc_uart project.
After build, use LPC_LINK2 to download the code to your MCB1857 board, the usb to com will work like this:

The code runs normally, and won't enter hardfault.
Wish it hepls you!
If you still have question with LPCXpresso IDE project, please let me know!
Have a great day,
Jingjing
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