You can set the MaxJsonLength property on your web.config:
[sourcecode language=”html”]
<configuration>
<system.web.extensions>
<scripting>
<webServices>
<jsonSerialization maxJsonLength="50000000"/>
</webServices>
</scripting>
</system.web.extensions>
</configuration>
[/sourcecode]
refer link: http://stackoverflow.com/questions/1151987/can-i-set-an-unlimited-length-for-maxjsonlength-in-web-config