Other than the fact that it's very difficult to figure out what's going on with that code, and some of it appears to be duplicating functionality in CI's User_agent library, it doesn't appear that anything in the code you've included is causing the error you've described.
I should point out, though, that loading a model via $CI->load->model($model) also instantiates the model, so the loader, more or less calls
Code:
$this->$model = new $model();
If you're doing something similar to the library, it could be the source of your problem.
Additionally, instead of this:
Code:
$CI->siter_page_sampler_library->save_stats($CID);
You should be able to call the other method like this:
Code:
$this->save_stats($CID);
