Hello Christophe,

In Web.Config file “Section” tag is used to enable application styling for entire Web application. By creating section tag with the name infragistics.web we are creating section for ig_reg .ig_res is a folder containing all CSS files for all the controls and by  writing following code in the web config file, you are providing the styling reference to the entire application .

In the Web.Config:

<infragistics.web enableAppStyling="true" styleSetName="Default" styleSetPath="~/ig_res" />

<section name="infragistics.web" type="System.Configuration.SingleTagSectionHandler,System, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />

You can refer the following document to find more information

http://help.infragistics.com/doc/ASPNET/2015.2/CLR4.0/?page=Web_Enabling_Application_Styling_Using_the_Web_Config_File.html

Creating new project for WebdatePicker has the same process as you creating a new website .Would like to know how did you added the reference of DLL in the new project? Are you getting any error message?

I have created a new project of WebDatePicker for your reference. Please find the attachment and let me know ifi may be further assistance.

I am able to reproduce the behavior. It doesn't have anything to do with the ig_res directory.  It has to do with using WebdatePicker controls in a page that inherits from a master page.  The WebDatePicker works fine starting from a blank web app, but it doesn't work when you choose to make an "ASP.NET Web Forms" application.  This is because it automatically generates a Site.Master file and the Default.aspx inherits from that

I have investigated your issue, and I have asked our engineering staff to examine this further.  To ensure that it will receive attention, I have logged this behavior in our internal tracking system with a Development ID of 220897 . The next step will be for a developer to review my investigation and confirm my findings or to offer a fix, or other resolution.

I will leave this case open and update you with any new information after the review.  You can also continue to send updates to this case at any time.

You can view the status of the development issue connected to this case by selecting the "Development Issues" tab when viewing this case on the web site. 

Please let me know if you need more information.