You put the wrong models in the wrong folder. Custom models are designed to replace specific characters, you can't just replace anyone with anyone. If you do, the bones (and thus the model) stretch and twist bizzarely.
What model/character were you trying to replace? And with what model/character did you replace it with?
it can also be messed up if they are outdated i downloaded some 1.1 models to 1.2.3 and it screwed up a bit, but also i downloaded a current version cell and it screwed up too. some files are currupted.