Did you connect a 10MikroFarad capacitor between Reset and GND to the Arduino on which you uploaded the 'ArduinoISP' Skech?
Furthermore: In order for your Atmega (target system) to run at 20MHz, the fuses must be set correctly. The easiest way to do this is to upload a bootloader designed for 20MHz. please make a circuit diagram that shows exactly what you have connected to the Atmege328 and also shows the connections to the Arduino Uno. A photo that shows the structure well also helps to see whether plan and reality match. this is the only way we can help you effectively.