Problems with a model

[eluser]Mat-Moo[/eluser]
I'm currently rewriting a website, and so far 90% of the work is done and working without issues. I've decided to add a new facility which calls some code that already works, but for some reason it just doesn't want to play ball. Even though I've tried to load the model in the code, it still doesn't play ball... e.g.

Code:

$this->load->model('groups_model');
        $users=$this->groups_model->get_group_users($groupid);

and I get

A PHP Error was encountered
Severity: Notice
Message: Undefined property: reminders_model::$groups_model
Filename: models/reminders_model.php
Line Number: 308

(crashing out on the $users=$this->groups_model->get_group_users($groupid)

The load model was added to see what happens as this is already loaded in the controller, and the same function called from another controller works 100%?

Any clues/ideas are welcome as I'm stuck on this now.