An A320 crew has an extended departure delay due to a recurring number 2 engine overspeed ECAM message. Efforts to 'clear' the software issue were not successful; resulting in a number 2 Fuel Management Unit (FMU) change.

Narrative

Extended delay due to number 2 Engine Overspeed ECAM [message]. We have a company bulletin for this issue. I am concerned that it was assumed; this is an Airbus glitch; and not a real problem. It appears that one of the solutions; (six start attempts); is beyond the scope of the Flight Manual (FM) limits without proper cooling time[for the engine starter]. In the Maintenance history; the aircraft had displayed the fault and was cleared. Then on the inbound flight the crew reported the same fault. Contract Maintenance cleared the fault and the flight attempted to operate. As soon as number 1 Engine Start Switch was placed to 'run;' we got the number 2 engine Overspeed message. After number 1 engine stabilized and we contacted Maintenance Control; the message cleared.Maintenance Control noted the problem; which broke [voided] the Maintenance Release (M/R) and then they issued a new M/R. As soon as we started number 2 engine; the number 2 Engine Overspeed ECAM message reappeared. Called Maintenance Control again and they advised to return to gate. Mechanics and parts were flown in on the XA:30 pm flight and apparently they first tried to clear the software issue; then changed the engine Fuel Management Unit (FMU). The problem did not clear. Line Maintenance indicates you need to start the engine three times for the message to unlock. Word of mouth in the mechanic group indicates it requires as many as six starts. On start number 5 the problem cleared. Apparently there has been a component change/upgrade and there is a conflict in the software that Airbus has not been able to solve.