The other day I waited 6 games to test my WIP map and when I finally got leader the file was corrupt. I quit out and selected the previous version. Also corrupt. In fact, every custom map I had in my repertoire was corrupted. Even my saved films and screenshots. Devastated, I joined a friend (Yacob521) who had recently played on the map, to see if he still had it in his temporary memory. He did, but he suggested something else; uninstall Reach from your hard-drive, and install it again. I did so, and it worked perfectly, every map I had was restored. I haven't tested this, but according to him it also fixes registry errors (loading the wrong map under the correct name).
Assuming this is true (and I don't see why you would lie), good find! You've actually just saved three of my maps, so thanks a bunch.
Credit goes to Yacob521 though, I'm just the messenger. According to him it fixes registry errors, but I haven't tested whether it does or not, all I know is it fixes "corrupt" files, ones that you can't even select that also have a warning symbol as their thumbnail.
A side-effect of Reach's horribly-designed file system. Seriously, when an iPod outperforms something running on the gaming powerhouse that is the Xbox 360... Bungie needs to patch this, but to adequately fix it, they'd probably have to completely redo the system from scratch. This, of course, would likely lead to total data loss for everyone who downloads such an update, so they probably won't do it.
Yeah, too dangerous. I just forge on a local network now--I haven't had any problems that way. If I want a friend to check out my map, I never save it, and I make any adjustments/suggestions he made myself on local.