Sometimes software unlock tools fail. For hardware-level recoveries, consider these:

Most chips have security levels:

If the previous flashing attempt crashed or lost power during a write cycle, the flash controller might be stuck in an internal busy state. When you connect a new programmer, the chip reports "ready," but the flash peripheral is locked. The RAM upload works, but the programmer can't execute—or worse, the RAM write fails because the system bus is partially wedged.

Once you’ve used an unlock tool to recover your device, prevent recurrence: