This is the number one cause of reflashing errors. Reflashing an ECU is a power-intensive process. The ECU must keep its processor running at full tilt to erase old memory blocks and write new ones. If the vehicle battery voltage dips below 12.0V—even for a split second—the ECU will cut power to the programming circuit to protect itself from corruption.
If you see 0x61, stop. Read the address. Unlock the region. Then, and only then, reflash again.