[Dovecot] Problems in auth when switching from PLAIN-MD5

Hi, i am running dovecot 2.0.11 (with mysql backend) and until now using PLAIN-MD5 as pass default_pass_scheme everything was working fine. However i wanted to change the pass_scheme to something stronger than plain-md5, so i started by reading the wiki.

I found this: http://wiki2.dovecot.org/HowTo/ConvertPasswordSchemes

But when i comment out "default_pass_scheme" and i create the pass with the {SHA256.hex} prefix i see this in the logs:

auth: Error: sql(xxx@xxxxxx.com,10.21.1.1): Password in passdb is not in expected scheme SHA256.hex

I tried with several algorithms, but it seems to be something in my config that it's only working with plain-md5. the auth_mechanism is plain with ssl/tls.

Maybe someone can give me a hint of where to see o which config file review.

Thanks in advance.

Eduardo.