Error- 403
From OS-Tan Collections Wiki
403-tan is one of the uncommon error-tans. Like the other error-tans, she wears a grey skirt and a white t-shirt. Her shirt says 403 Forbidden on it. As well, like the other error-tans, she also has her blue hair in pig tails. There is also a another version of 403-tan but it's only a photoshopped version from a 404-tan image.