Admin panel user section error…

capabilities.php code details below

//Build $allcaps from role caps, overlay user’s $caps
$this->allcaps = array();
foreach($this->roles as $role => $value) {
$role = $wp_roles->get_role($role);
$this->allcaps = array_merge($this->allcaps, $role->capabilities);
}
$this->allcaps = array_merge($this->allcaps, $this->caps);
}

I am fairly sure that is code from 1.6
The forums do not support 1.6 code at all.
The only place you can ask for support – because none is promised – is the testers list:
https://codex.www.ads-software.com/Mailing_Lists

If that were my blog, I would backup and reinstall 1.5.1.3
Backing up before you do anything else is a Good Thing.

To confirm, the above is 1.6 code. capabilities.php doesn’t even exist before 1.6. As Podz said, 1.6 is unsupported, and the only reason you should be using 1.6 is if you are a test (in which case this post belongs on the WP-Testers mailing list) or if you are capable of writing PHP in your sleep (in which case patches belong at https://trac.www.ads-software.com/ )