I'd need to go look them up (which I'm too lazy to do right at the moment), but as I recall, one of them failed due to outgassing of something or other. Obviously, that's a solvable problem since we already know how to build sealed modules for the space station that do not have outgassing (i.e. materials) problems. The other, I think, failed because the crew were having problems, not because the structure itself failed. If you know otherwise, that'd be interesting to know.