There are many things that could cause such problems. The far most common ones are:
- The MCU could be secured. This is a feature of new MCUs that prevents copycats from stealing code. You can unsecure your MCU through a free program available from PE Micro's web site, or through the Codewarrior debugger.
- Incorrect BDM or reset lines. Missing pull-ups on these lines. Missing ground between BDM connector and PC.
- 2x3 socket header turned upside down 180 degrees, or the cables/connectors are damaged.
- CPU clock is missing because of wrong design or poorly soldered crystal. Make a rough measurement of the oscillator frequency with an oscilloscope to see that the MCU is alive and running at the desired speed.
- Poor power supply or no supply at all.