HD Install :: an error occured updating the password file

after instal in hd and change the root password i get the follow error

passwd[29]an error occured updating the password file

i`m newbie in linux and i have a low machine ...
Cyrix 150 mhz motherboard pcchips 100 96mb ram and quantum bigfoot 1.2 gb

jeje is a very low machine but in live cd mode this work great...audio sound video firefox etc..

i decided install to hd but i can`t

Thanx

Paulo
Chiloe, Chile