The URI you submitted has disallowed characters.

[eluser]Bhavani Shekhawat[/eluser]
[quote author="Burak Guzel" date="1276052640"]You just need to remove the "<form>" from your view (the first line).

You are already calling form_open(), which correctly creates a POST form tag, instead of the default GET (which causes the error you are having).

Another unrelated problem: Your form_open() links to 'site/add_artifact', while in fact your controller is named 'site/add_artifacts'.[/quote]

Problem solved. It was the <form> thing. Thanks a lot man!
p.s. thanks for the artifact typo too!