I am upgrading asp.net webform project which uses 14.2 dll with 21.1.

I removed older references of the dll and added 21.1 . I have removed all the older dll's from bin and obj and rebuild the project to make sure all the old referenced dll's are gone and clean the solution and rebuild the solution.

However, I am still getting "Ambiguous match found." because of WebDropDown controls. Below is the snippet of the controls.
<ig:WebDropDown runat="server" SkinID="skingdropDown" AutoPostBack="false" StyleSetName="test"
Width="200px" Height="20px" ForeColor="#333333"
backcolor="white">
<Items>
<ig:DropDownItem CssClass="ig_ListItem"></ig:DropDownItem>
</Items>
</ig:WebDropDown>

Could please help me in finding what function is Ambiguous as error do not give more information apart from this message.

Thanks in advance.