problem with RegisterClientScriptBlock in UpdatePanles

Error:::::
The script tag registered for type 'ASP.projectviewer_asp' and key ###### has invalid characters outside of the script tags: <link href='####.css' type='text/css' rel='stylesheet' >. Only properly formatted script tags can be registered.

This Work fine -------------
page.ClientScript.RegisterStartupScript( page.GetType(),"CSS", " <link href='####.css' type='text/css' rel='stylesheet' >", false);