Ubuntu :: Missing Critical Shared Libraries Becoming Corrupted?

Fascinatingly weird one here. First, this issue isn't on my computer, it's from someone who I am helping. I don't have first-hand access to the computer. Some background: the machine originally had Ubuntu Hardy, which we upgraded to Lucid a couple of weeks ago. Earlier this week, he gave me a call that Ubuntu wasn't booting up; it dropped to the command line. Some tinkering later, I figured out that libgthread-2.0.so had become corrupted, so X wasn't starting. It gave an error complaining that it had an invalid ELF header.I figured that this was just an odd freak occurrence; there was a bad kernel panic previously, so maybe the library was upgraded and the system was just writing to the disk at that time. Fixed via sudo aptitude reinstall libglib.

Ubuntu then started and everything ran perfectly. Today, he gave me a call. After he had restarted the computer, Ubuntu again dropped to terminal at the same point while booting. I had him open a new tty and run startx, which failed with a different shared library but the same error: libXext.so.6 has an invalid ELF header!

We had run updates, but I don't recall whether X's shared libraries were touched. Even if they were, though, that shouldn't affect anything. There were no hard resets between my fixing libgthread and libXext breaking. I'm going to try a clean install; I'm really just hoping we can figure out why this is, because it's an amazing little problem.