I have a problem with new module

[eluser]huutri[/eluser]
This is code in view layer in new my module:
$this->load->module_model('productcategories','mproductcategories');
$listcate = $this->mproductcategories->GetAllCategories('vn');

I get a error: "A PHP Error was encountered
Severity: Notice
Message: Undefined property: CI_Loader::$mproductcategories
Filename: views/index.php"

"Fatal error: Call to a member function GetAllCategories() on a non-object"

Can you explain to me how to call a function in model from view layer in a module. Thanks you very much