Here is a notice when using blhost to program KL03.
To program KL03 by blhost.exe, user will get the flash is in security state as below message:
Input 1: blhost.exe --p com47,38400 -- get-property 17
ping responded in attempt(s)
Inject command 'get-property'
Response status=0 <0x0>Success
Response word1=1 <0x1>
Flash Security State = SECURE
Input 2: blhost.exe --p com47,38400 -- flash-erase-all
Ping tesponded in 1 attempt(s)
Inject command 'flash-erase-all'
Response status=10001 <0x2711>Command disallowed when security is enabled
The symptom is similar to programming fail by BDM in some cases. The solution is down BDM speed.
So set the baud rate speed down to 9600 with each command and the problem is gone.