Seems like you have mod_security enabled on your server, contact your hosting provider to disable it.
Where I can see mod security? Perhaps one screenshot could solve my problem.
Ask another question: how to legally remove a label Oxwall Software from my website. How to do it correctly technically and legally?
As to your question - all you need to donate $50 to Oxwall Foundation, as soon as we process your payment, we'll add you to the donators list (which makes you eligible to remove Oxwall attribution link) and provide you with the instruction hwo to remove it.