c# - Entity Framework Code First - Cannot insert duplicate key in object 'db' -

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I'm using the new EF code in my project first, and I'm getting a weird error, my mode is : 

  abstract class members {public virtual member of public; ... some other stuff} Class users: Members {public virtual string name; ... some other props are not defined by a new key} Category MyDbContext {public DbSet   
 The result of deployment on SQL Server is fine, I have a member table and a user table (TPC). Now in my main I have the following code:  
  Fixed main () {User X, Y; (MyDbContext ctx = new MyDbContext ()) using {x = ctx.Users.Create (); Y = ctx.Users.Create (); X.Name = "SomeUser"; Y.Name = "SomeUser2"; Ctx.SaveChanges (); }}   
 I save changes:  
 
 "Unchecked exception: System.Data.Entity.Infrastructure.DbUpdateException: An error occurred while updating the entries See Internal Exceptions for Hui De Tuq. ---> System.Data.UpdateException: An error occurred while updating the entries. See internal exceptions for details. ---> System.Data.SqlClient SqlException: Violation of primary key 'PK_  user  _0CF04B1821B6055D'. Duplicate in item 'dbo.users' The key can not be inserted. "  
 By default, MemberId is identical, so I'm just not seeing what's happening here, I tried to create an example with new ones And attach them in context, but the error was similar, any thoughts?  
 EDIT: Remember to tell that the member is an abstract class that is competing. 
 
 
 I tested it and the table of derivatives generated in TPC  (table per concrete type)  PK has not been defined as an identity in EF 4.1 in R.C.

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