Thank you very much alistairmuir for your reply. I do really appreciate it.
First, let me say that both BKGD and RESET pins have external pull-up resistors (10k and 15k, respectively).
The RESET pin has also a decoupling (pull-down) capacitor too (1000 pF).
Both of these pins are connected only to 6-pin BDM header and the IC itself, and nowhere else.
For the exact states of the BKGD and RESET pins, I should probably use a digital oscilloscope to monitor the toggling of their states. But for now:
Both the BKGD and RESET pins are "High" after POR (probably due to their pull-up resistors).
However, after I press the debug/erase button at CodeWarrior, the BKGD pin goes "Low", and the "power-cycle" dialog appears.
I turn off/on the MCU, as the "power-cycle" dialog suggests, and press OK; then the BKGD pin goes "High" again.
After a few seconds, the CodeWarrior gives the following error:

If I press "Retry", the same procedure happens again: the BKGD pin goes "Low", and the "power-cycle" error occurs!
During all these procedures, the CodeWarrior logger console writes the following logs:
Frequency change to ~0hz.
Frequency change to ~0hz.
Frequency change to ~0hz.
Frequency change to ~0hz.
Frequency change to ~0hz.
Error: Can not enter background mode .
Frequency change to ~0hz.
Frequency change to ~0hz.
I guess the problem could be related to the internal clock generator (ICG) of the MCU. How should I know if it's working properly?
I hope somebody helps me find the solution to this challenging problem. :smileysad: