i cant say for certain but i would guess you ran out of fuel…BUT you had fuel remaining , well yes but if you look more in detail at Concordes tanks it has a lot of fuel tanks but only some feed the engines directly so you may have had fuel stuck in tanks that are not connected directly to the engines . ( i cant remember the numbers but i think its tanks 5 and 7) This is where the dark art of moving fuel around in Concorde comes from also what isn’t mentioned in the manual and caught me out is that you need to transfer fuel to tank 11 for CG purposes but you also need to replenish the tanks feeding the engines from the forward tank . last time i flew it i was constantly looking at the MSFS fuel load tool in the upper bar to assess what fuel is left in which tank to make sure those feed tanks don’t run dry.