firmware file corrupt?????!!!!

ok i have an origional ipod nano. i just recently got a new computer too. so when i went to get itunes i got the latest version (its very kool too) and it says that i need an update for my ipod... so i update it. as the update downloads im waitin... and when its finally done downloading it says "firmware file is corrupt." so i dont kno what to do! i mean i havent done anything to it! the same with my sister's ipod nano.

can anyone tell me y this is happening?!?