XSS Protection Problem - it blocks the page

[eluser]xcristi[/eluser]
Hello,

Well, I turn on the XSS protection in CI configuration for automatic clean up. When I enter something nasty in a textarea, the filtering seems to work (?) but I get only a blank page as a result. The error thrown in logs is:

Code:

PHP Fatal error:  Call to undefined function:  get_instance() in /home/html/soimul/system/libraries/Input.php on line 855

I turn off this feature and try with some manual clean up ($this->input->post('field', 'true')) and it works very well. I can go on and use it this way, but it will be more convenient to do it automatically.

What do you think it's wrong in the first case?
Thanks.