“Error on Decrunching” when extracting with Unarch

when i download a .MP4 file, i get this error while trying to extract..its very frustrating..can anyone help? im using snow leopard
Answer #1
anyone???
Answer #2
Your file is corrupted,if you have multiply archives just double click on first,use other unarchiver like 7z or stuffit expander.
Answer #3
file isnt corrupted, a friend using windows downloaded the same file and it works fine..