Error: Trait 'Illuminate\Validation\ValidatesWhenResolvedTrait' not found. When hosting site.

Hello,

I've just uploaded my website to my shared hosting, and I'm getting this error when I'm trying to load a page.

  FatalErrorException in FormRequest.php line 19:
  Trait 'Illuminate\Validation\ValidatesWhenResolvedTrait' not found

I've read that changing this line:

  use Illuminate\Support\Facades\Validator;

To this:

  use Validator;

That is would fix the error but that didn't work for me. I hope someone can help me with this problem. I'm using laravel 5.3 and PHP version 5.6.30.

Thanks in advance, Bram