Error: The underlying provider failed on Open in ASP.Net MVC

Dear All, I create the webapplication in .net using MVC framework 5.0. In that application i am using already Two ADO .Net Entity Data Model(.EDMX) file for using Linq To Sql.Whenever i tried to Using thid ADO .Net Entity Data Model(.EDMX) File From and in that file i am using More than 250 Tables.Whenver i tried to Execute this one using Linq then I Get the Error "The underlying provider failed on Open."  Please give me the Suggestion. 

Regards

Sandip