Entity Framework Exception "The underlying provider failed on Open"

Question

I have created a windows service which listen to a TCP/IP port and save received data in database using Entity Framework. Most of the time it works fine but some time its throwing an exception "The underlying provider failed on open." on save data in database. Here is my exception details:

    Exception: 2/27/2014 10:31 AM:
    The underlying provider failed on Open.
     at System.Data.Entity.Core.EntityClient.EntityConnection.Open()
     at System.Data.Entity.Core.Objects.ObjectContext.EnsureConnection()
     at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
     at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClassb.<GetResults>b__9()
     at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
     at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
    at System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0()
     at System.Lazy`1.CreateValue()
     at System.Lazy`1.LazyInitValue()
     at System.Lazy`1.get_Value()
     at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()
     at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
     at System.Data.Entity.Core.Objects.ELinq.ObjectQueryProvider.<GetElementFunction>b__1[TResult](IEnumerable`1 sequence)
     at System.Data.Entity.Core.Objects.ELinq.ObjectQueryProvider.ExecuteSingle[TResult](IEnumerable`1 query, Expression queryRoot)
     at System.Data.Entity.Core.Objects.ELinq.ObjectQueryProvider.System.Linq.IQueryProvider.Execute[TResult](Expression expression)
    at System.Data.Entity.Internal.Linq.DbQueryProvider.Execute[TResult](Expression expression)
    at System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source)
    at Service.DemoService.Save(String received, TcpClient client)

What is the thing behind this exception and how to resolve it?

Answer 1

Usually, when working with Entity Framework you'll need to enable the multiple active result sets option in your connection string by setting MultipleActiveResultSets to true as follows.

<add name="conn" 
  connectionString="
    Data Source=.\;
    Initial Catalog=TDB;
    UID=admin123;
    PWD=123;
    MultipleActiveResultSets=True"
  providerName="System.Data.SqlClient" />

Verify that it solves your problem.