Microsoft Reporting Services for web provides default cascading style sheets (.css) files that is embedded and defines styles for the report toolbar in HTML Viewer and Report Manage. If you want to customize the report toolbar as your own styled control like your own color, font and layout of items, you must be struggling to adjust style sheet for reportviewer. In the meantime a web developer are working on css file, sometimes faces with weird situation seeming never revealing why stupid error happens after it perfectly worked. After publishing an web application to an IIS 7.0 server, The Toolbar which worked nicely is completely broken and showed up something like this,