When you call stored procedure with select and output parameters and you don't select on some conditions (for example, you're just returning an error code) — you get a mapping EntityCommandExecutionException. This package fixes this annoying behavior of EF by returning empty data set and letting you read output parameters. Example: Consider you have this sql procedure: CREATE PROCEDURE [dbo].[Foo] @Condition int = NULL, @ResultCode Int = NULL OUTPUT AS BEGIN IF @Condition IS NULL BEGIN SET @ResultCode = 1; -- return 1 if condition = null RETURN; END SELECT 1 as 'One', 2 as 'Two'; -- select otherwise SET @ResultCode = 0; END Calling this procedure in EF: var resultCodeParameter = new ObjectParameter("ResultCode", typeof(int)); var result = db.Foo(null, resultCodeParameter).FirstOrDefault(); var resultCode = resultCodeParameter.Value; will throw an exception: System.Data.Entity.Core.EntityCommandExecutionException: The data reader is incompatible with the specified 'xxx.Foo_Result'. A member of the type, 'One', does not have a corresponding column in the data reader with the same name. Calling EntityFix.Load() once on your application start will fix this bug.