Good morning.
You don't have to enable it for all the users, its enabled by default. You can look at the user table of your database, the karma is 1 for all.
I'm going to look at the rest of your posts now. :)

I also didn't like the rep system, this is why I made this on the first place.
In this, you don't rate the posts, you rate the users. And you can't rate someone more than once (if you do, the new vote will replace the old one).

Rating via the postbit uses the same code as rating via the profile. It's just links. They take you momentarily to karma.php, which processes the vote, checks permissions and everything and takes you afterwards to the user's profile (I should make the postbit one via AJAX on the next version, if I ever learn AJAX good enough :p)
Check if the appropriate time has passed when you are trying to vote someone. That time is configurable via the settings. Most e-steki Karma settings apply to the admin as well (as I was mad when the other admin on my site turned his karma off :p)

These settings are already there, look at the screenshots ;)

Btw check if the sceduled task has been added, as I've never have made before a sceduled task in a product of mine.

Okay, I'll check the time in between rating, but I don't think that I rated a single person.

edit: I chanded the minimum time between rating 2 different users to 0
changed can rate self to yes, ignore users that haven't visited for x days to 0

and I still can't rate anyone.

:(

Then its not it.
in your karma.php find:
add below that:
Then vote again and paste me the message that is echoed at the top (don't forget to remove the line afterwards).

Userid: 70 Karma banned: Restricted: Banned: TimeOK: 1 UsersOK: 1

That's really weird :confused:
Thanks, I'll look into it.

Are you trying to rate yourself?