PS3 won't read Resistance 2 disk

[air_max]

OK, I started this thread because my ps3 would not read the R2 disc. it showed up on the XMB just fine, the background screen showed up when the cursor was over the disc icon, music played etc. started the game, nothing. ejected the disc, wiped it off, worked. went to campaign to continue (haven't beaten it yet [i know!!!]), no continue option. checked my saved game files, no save file, just a corrupted data where im pretty sure the r2 should be. anyone??

Edit: luckily, i back up all my save game data frequently. popped in the SD card, found my R2 data, copied it, loaded up the game, continue option there from where i left off.

anyone know why this would happen?