Bx3105 gives "connection failed - 103" when trying to upgrade to rev2.7.3 from rev 2.63 using "BX31xxBlTest.exe and com04

When trying to use “BX31xxBlTest.exe com04 -u BX310x.2.7.3.bin” to update a bx3105 from rev 2.63 to rev 2.73 I get a response
C:\Users\User\BXPROG>BX31xxBlTest.exe com04 -u BX310x.2.7.3.bin
connection failed -103

I have checked and com4 does exist and is connected to the device input.
what does this mean? Do you have more detailed information on the process and possible errors.
I have done this procedure successfuly several times and had no problem in the past.

For fw upgrade, I remember there is a gpio27 needed to be set HIGH before power on.

you can also use "BX31xxBlTest.exe com6 -v " to check the connection after setting the GPIO27.