The final solution to the problem of SYS undefined in the new Ajax version

If this problem occurs, search Baidu for the web. config problems, you can use my web. config looks like there is no problem; there is no other way to regenerate a new web. config, the problem persists.
The final solution is to move the following to the function, that is, to call the function after loading the page. The problem is solved.
VaR PRM = SYS. webforms. pagerequestmanager. getinstance ();

The following describes the Modification Scheme of Web. config for future use.
First, set the configuration in Web. config:
..............
<Httphandlers>
<Remove verb = "*" Path = "*. asmx"/>
<! --
<Add verb = "*" Path = "*. asmx "Validate =" false "type =" Microsoft. web. script. services. scripthandlerfactory, Microsoft. web. extensions, version = 1.0.61025.0, culture = neutral, publickeytoken = 31bf3856ad364e35 "/>
<Add verb = "get" Path = "scriptresource. axd" type = "Microsoft. Web. Handlers. scriptresourcehandler" Validate = "false"/>
-->
<! -- Change the above name to the 1.0 RC version. The namespace has been changed to System -->
<Add verb = "*" Path = "*. asmx "Validate =" false "type =" system. web. script. services. scripthandlerfactory, system. web. extensions, version = 1.0.61025.0, culture = neutral, publickeytoken = 31bf3856ad364e35 "/>
<Add verb = "get" Path = "scriptresource. axd" type = "system. Web. Handlers. scriptresourcehandler" Validate = "false"/>


</Httphandlers>
<Compilation DEBUG = "true">
<Assemblies>
<! --
<Add Assembly = "Microsoft. Web. Extensions, version = 1.0.61025.0, culture = neutral, publickeytoken = 31bf3856ad364e35"/>
As follows:
-->

<Add Assembly = "system. Web. Extensions, version = 1.0.61025.0, culture = neutral, publickeytoken = 31bf3856ad364e35"/>
</Assemblies>
</Compilation>

............

Recompile and run.

If an error still persists after web. config is configured, set <asp: scriptmanager id = "scriptmanager1" runat = "server" asyncpostbacktimeout = "200">
</ASP: scriptmanager>
Followed by the <form> flag.