Don't Login after upgrade

HI all,
i have make upgrade from 4.1 to last one, all upgrade procedure work well.
At first Login ask me to change user and adeguate a password to new policy,
and now i can't login !
My mistake it's not clean temp dir as indicated in the upgrade page, unfortunately i don remember which dir must be cleaned if this is error.

Someone can help me, because need to enter very urgently.

Tnx
Enrico

Thanks for quick answer