Check in device manager for com ports, on my PC it is a quite higher number.
I had the same problem...
I had my created my own bootloader which gave me these errors. I then loaded the example bootloader project from the zip file in the like below.
I tried using the Bootloader host tool in the PSoC creator 4 and it work after using the UART_Bootloader project and it worked fine.
also make sure that you have your application start the bootloader process. (use Bootloadable_Load(); )