because I had thee same problem back when I had GT5, I had 2 PS3 and I had installing problems on both consoles and I ended up buying a new GT5 disc , problem fix for me.Why would update data coming from an online server be affected by the state of the game disc? The updates are installed on to the HDD.
And for those that say "well I have no problem" doesn't help to resolve the issue nor does it mean the problem doesn't exist.