error showing cant implecitly convert coi to string

I think the error comes from the method argument. the method JoinTab accepts a single argument of string type, therefore you should call this method with a string parameter and not without parameter (parameterless). so your calling code should be like this: Grid1.DataSource = x.ToList(); Grid1.DataSource = objrepo.JoinTab (strParam) where strParam could be any useful string-type variable. secondly, you can make your JoinTab(string s) method parameterless by deleting everything inside the open and close bracket. i.e to declare your method as parameterless do it as below public void JoinTab () { ....... ........ } I this will help.