[oe] proftpd 1.3.5 cannot authenticate with any user

[Cjb_SW Freescale]

Hello,
I am facing some problems with Proftpd and I cannot login with any user.
I am aligned with poky 1.8, and the version of proftpd is 1.3.5
The ftp client can connect to the server, but with the "correct"
password I get an error 530 Login Failed.

The only thing that I changed from the standard configuration, is the line:
RootLogin  on

I know that I shouldn't do it, but I really need it.
Anyhow, I tried also other users, and passwords, nothing works.

Any suggestion?
Thank you
Simone