It doesn't always mean that your uC is faulty. Most often you get this error if your programmer is faulty. If you are using a serial port based programmer that draws power from the port, then the chances of error are more. This is because all serial ports does not work at exactly +-13V as RS232 standard states. Mine works at +-10V. So if this is the problem, I guess your device is not programmed at all or may be some errorneous data is being written to it. Use good quality programmers.