Hi,
this is caused because too much data return in the SQL Query behind the web service call, so the web service returns an error. A simple change to the web.config file can increase the size limit of data returned.
Add following code in your web.config file
<system.web.extensions>
<scripting>
<webservices>
<jsonserialization maxjsonlength="5000000" />
</webservices>
</scripting>
</system.web.extensions>
Hope this will help you
Best Luck
Happy Coding:)