Limits to multiple Eloquent relationships ?

I have a number of different roles, who are all essentially "users" in my laravel app.

I'm having a problem with eloquent relationships where I can easily get one of the relationships, in the context of the user as a car owner, but when I try get another relationship in the context of a (different) user as a maintenance manager, I get this error: Cannot redeclare class App\Models\User.

serviceAgreement model

public function manager()
    {
            return $this->belongsTo('carfreak\Models\User','manager_id','id');
    }

Works fine:

$managers = $owner->serviceAgreement()->get();

produces error

$managers = $owner->serviceAgreement()->with('manager')->get();

I'm thinking the problem lies somewhere in how I've written my relationship - my referring to the \Models\User. I've tried to refer to the logged in user, but it (a) doesn't make sense for this application and (b) doesn't work anyway.

return $this->belongsTo(Auth::User(),'manager_id','id');

Some pointers please?

via Chebli Mohamed