A Lead Mechanic reports the #1 engine fuel flow meter was replaced due to leaking on an A320. He was able to get their aircraft maintenance history and parts compatibility computer data system to accept the part tracking tag number and serial number data into the computer system; even though the part was later found to be 'not effective' for the aircraft.

Narrative

A320-200 had the #1 engine fuel flow meter replaced due to leaking. A non-effective part was installed. I entered the log page into our aircraft maintenance history and parts compatibility computer data system for mechanic 'X'; who (had) installed the part. The computer system did not take my entry the 1st time. An alert page had appeared; because I entered the wrong serial number (S/N). Another Mechanic at that time was sitting next to me. I asked him for the correct S/N he installed on the aircraft. He told me the S/N he installed. I went back to the computer and pause/break out of the alert page. I went back to the log page thru the parts system and entered tracking tag number and S/N. The maintenance parts compatibility computer should (have) kicked back the alert page; because tracking tag number and S/N number does not match. Instead; the computer took my second entry. After computer took my second entry; I did not take any further action; because the computer system took my entry the second time.