Since the switch to Multi Enrolment in 1.6, Manual enrolment is enabled by default and you can't disable it through the user interface.
In 1.5, if you were using Database enrolment for example, you could disable manual enrolment if you decided so. In fact, this is what we did.
I know I can disable the Manual enrolment plugin changing the database directly, but I wonder why this is so. I mean, what is the reason to make the manual plugin always enabled?
Saludos. Iñaki.