In this blog I will try to summarize
the most common reasons for getting
the famous 'Sys is undefined' error when running an Ajax enabled web
site or application (there are almost one milion results on Google for that phrase). Where does it come from? In every Ajax web pages source you will see a code like this: <script type="text/javascript"> //<![CDATA[ Sys.WebForms.PageRequestManager._initialize('ScriptManager1', document.getElementById('form1')); Sys.WebForms.PageRequestManager.getInstance()._updateControls([], [], [], 90); //]]> </script> This is
the initialization script of
the ScriptManager. So, if for some reason
the Sys namespace is not available when
the code executes you get
the Sys is undefined error. Here are
the most common reasons and solutions for that problem: 1.
The error occurs when you have added a control from RadControls for ASP.NET AJAX, but your application is not configured to use ASP.NET AJAX.
For example, in VS 2005 you created a new Blank
Site instead of a new Ajax-Enabled Web
Site and
the Sys is undefined message pops up.
To fix it you need to follow
the steps described at Configuring ASP.NET Ajax article (check
the topic called Adding ASP.NET AJAX Configuration Elements to an Existing Web Site) or simply create
the Ajax-Enabled Web
Site. You can also check my other blog post on
the matter: Visual Studio 2008: Where is
the new ASP.NET Ajax-Enabled Web
Site template? 2. Authentication - as
the website denies access to all pages to unauthorized users, access to
the Telerik.Web.UI.WebResource.axd handler is unauthorized (this is
the default handler of RadScriptManager). This causes
the handler to serve
the content of
the login page instead of
the combined scripts, hence
the error.
To solve it - add a <location> section to
the application configuration file to allow access to Telerik.Web.UI.WebResource.axd to all users, like: <configuration> ... <location path="Telerik.Web.UI.WebResource.axd"> <system.web> <authorization> <allow users="*"/> </authorization> </system.web> </location> ... </configuration> Note that
the access to
the standard ScriptResource.axd and WebResource.axd is automatically allowed for all users (authenticated and unauthenticated), so if you use
the ScriptManager instead of RadScriptManager - you will not face this problem.
The authentication problem does not manifest when you disable script combining or use
the CDN. Adding
the above configuration section will make it work with RadScriptManagers combined script. 3.
The IE6 browser fails to load
the compressed script.
The problem does not appear in any other browser. There is a well known bug in
the older versions of IE6 which lose
the first 2,048 bytes of data that are sent back from a Web server that uses HTTP compression. Latest versions of RadScriptManager does not compress
the output at all if
the client is IE6, but in
the previous versions you need to manually disable
the output compression to prevent
the error. So, if you get
the Sys is undefined error in IE6 - update to
the latest version of RadControls or simply disable
the output compression. 4. Requests to
the *.axd files returns Error Code 404 - Not Found. This could be fixed easily: Check in
the IIS management console that
the .axd extension (the default HTTP handler extension) is allowed:
Also check if
the Verify if file exists checkbox is unchecked (click on
the Edit button appearing in
the previous screenshot to check). More information can be found in our troubleshooting article and from
the ASP.NET QA team blog post 5.
The virtual directory in
IIS is not marked as Web Application. Converting it to Web Application should fix
the problem. 6. Check for
the <xhtmlConformance mode="Legacy"/> option in your web.config and remove it. It would be rather rare to become a victim of this exact case, but still have it in mind. Scott Guthrie describes it in more details In
the above points I mentioned several times
the terms web resources, javascript output, compressed script. If you want to find out more about these please see
the Web Resources Demystified series of my friend and colleague Atanas Korchev I hope that one of
the above solutions will help you get rid of
the Sys is undefined error. Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.
