Hello Sreevani,

Thank you for posting in our community.

I believe the reason for your issue is the fact that the is replaced by tag for WebTab. For example, if you would like to add a button in one of the content tabs  this could be achieved as following:

<ig:WebTab ID="WebTab1" runat="server" Height="200px" Width="300px">
 <Tabs>
 <ig:ContentTabItem runat="server" Text="Tab 1">
 <Template>
 <asp:Button ID="Button1" runat="server" Text="Button" />
 Template>
 ig:ContentTabItem>
 <ig:ContentTabItem runat="server" Text="Tab 2">ig:ContentTabItem>
 Tabs>
 ig:WebTab>

Additionally, I noticed that you are using the ThreeDEffect property which is not available in WebTab as well. The corresponding styling could be achieved with BorderStyle property. Some further reference about WebTab class members could be found at:

http://help.infragistics.com/Help/Doc/ASPNET/2014.1/CLR4.0/html/Infragistics4.Web.v14.1~Infragistics.Web.UI.LayoutControls.WebTab_members.html#

Some further reference about Using WebTab could be found at:

http://help.infragistics.com/doc/ASPNET/2014.1/CLR4.0/?page=WebTab_Using_WebTab.html

I hope you find this information helpful.

Please let me know if you need any further assistance with this matter.