Can't create user account

Hello all,

I'm moodle admin and recently i update the moodle version from 1.9 to 2.6.

Everything goes well but now the moodle don't allow visitores create manual accounts (and this option is enabled)... and even when i (administrator) try to create an account ussing site manager, create new user account.... after fill all the fields and submit data, it apears an error of "page not found"

Any help or suggestion for this situation????

Thanks