Authentication... to be continue 3... and other routine

Hi,
I have spent a lot of time and strengths to make the aithentification and validation on the forms where it needs:
1. Login form (checks if the user is activated)
2. Activate form
3. Some enhancement of register page's design
4. Validating everywhere...
huh!
And the last trouble I have is .... "You must specify a non-autogenerated machine key to store passwords in the encrypted format. Either specify a different passwordFormat, or change the machineKey configuration to use a non-autogenerated decryption key."
It's because I tried to use only the encrypted password instead hashed. And what should I do now? I don't know yet.... just now I want to sleep...
Bye
Time spent: 4,5 hours