I know some will say upgrade to 2.4G system but anyhow....I have KO EX10 with RF502 Super Module in 40Mhz and its glitching like crazy. I also have RF501 Professional module (a friend borrow it to me) which works flawless. My question is what are the differences between these 2?

75Mhz they are different frequencies.

Both modules are in 40Mhz.

just newer and older models and the rf502 is the fastest of its kind they claim 30% faster than the501 in hrs mode..

Any special instruction when I m using this 502FS module, coz mine is almost brand new and its glitching very bad.

nothing special really, its all in the manual and safety guidelines
im sensing its the TX module that giving u this headache. try to use it in normal speed mode with rf502, some just let go the moment u set it to hrs mode. email ko-propo for warranty claim, prepare for bloody long journey back to Japan