TaskQueue.php Error - Laravel 5 & Forge

When running any Posts and Model::create function within Laravel I am being greeted with the below error;

FatalErrorException in TaskQueue.php line 13:
Interface 'GuzzleHttp\Promise\TaskQueueInterface' not found

This was working perfectly fine on my local machine but as soon as the website was put onto a server with Forge it has started to show this error.

It looks like the server is trying to use the Queue function with Laravel but my code doesn't ever make use of this;

public function postCreateCustomer(){
        $input = Request::all();

        $customer = Customers::create([
            'customer_name'      => $input['customer_name'],
            'customer_url'     => $input['customer_url']
        ]);

        $password = str_random(8);
        $pass = Hash::make($password);

        $user = User::create([
            'name'      => $input['name'],
            'email'     => $input['email'],
            'password'  => $pass,
            'user_type' => 3,
            'active_customer' => $customer->id,
        ]);

        Access::create([
            'user_id'     => $user->id,
            'customer_id' => $customer->id
        ]);

        $the_content = '<p>Hello '.$input['name'].' ('.$input['customer_name'].'),</p>
        <p>Thank you for creating an account. </p>
        <p>Your login details are listed below;</p>
        <p><strong>Username</strong>: '.$input['email'].'<p>
        <p><strong>Password</strong>: '.$password.'<p>';

        $contactEmail = $input['email'];
        Mail::send('emails.default', ['the_content' => $the_content, 'the_heading' => 'Customer Account Created'], function ($message) use ($contactEmail) {
            $message->subject("Customer Account Created");
            $message->to($contactEmail);
        });

        Session::flash('success_message', 'The new customer has been created.');
        return Redirect::to('/customers');
    }

via Chebli Mohamed