I'm afraid I don't have the answer, but I'm not surprised its choking on a 2.5 GB
file - Photo gallery is after all only a basic "look see" application.
IrfanView is a decent free picture editor - I don't know if it can cope with 2.5
GB pictures but I've used it successfully with a 1.9 GB picture. Worth a try, I'd
say.
BTW that TIFF is probably at a far higher resolution than the original, which is
a bit pointless really.