Please check the following steps in order to resolve the modal popup issue.
1. Check the browser console for any error.
2. Verify the AjaxCotrolToolKit dll is copied to the server or not.
3. Check the css are loaded or not in the browser.
4. To use PageMethods, you will need to make sure that you have enabled the following:
- EnableSession attribute on the WebMethod.
- ScriptManager control on the page.
- EnablePageMethods property on the ScriptManager control.
5. Remove router settings in web.config and adding to httpmodules section if you are using routing.
<add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
6. Add the following in the web.config file.
<pages>
<controls>
<add tagPrefix="ajax"
namespace="System.Web.UI"
assembly="System.Web.Extensions,
Version=1.0.61025.0,
Culture=neutral,
PublicKeyToken=31bf3856ad364e35"/>
</controls>
</pages>