Solution - For this type of problem you should use same assembly version number in web.config file and add same version assembly in add reference and use same version assembly in aspx page <%@ Register assembly="Infragistics4.Web.v13.1, Version=13.1.20131.2157, Culture=neutral, PublicKeyToken=7dd5c3163f2cd0cb" namespace="Infragistics.Web.UI.GridControls" tagprefix="igtbl" %> then version number defined above 13.1.20131.2157 should be same at below three places. Web.config File Add Reference Aspx Page