Modify Web.config

Attention Please:

Project base on .Net 4.0, you must add two properties controlRenderingCompatibilityVersion and clientIDMode to <page> tag.
    <pages controlRenderingCompatibilityVersion="3.5" clientIDMode="AutoID">
        <controls>
        <add assembly="FineUI" namespace="FineUI" tagPrefix="ext" />
        </controls>
    </pages>
    

Also be careful of Newtonsoft.Json.dll version:

FineUI.dll only has one version for .Net2.0, which can be used in project based on .Net2.0, 3.5, 4.0.

However Newtonsoft.Json.dll has separate versions for different .Net versions.
If your project is based on .Net2.0, please reference the file json.net\Net20\Newtonsoft.Json.dll; If your project is based on .Net4.0, you should reference the file json.net\Net40\Newtonsoft.Json.dll.