Validation failed for one or more entities. UserManager.AddToRole() - asp.net

Question

I'm developing a Web Api using ASP.NET MVC5 and I have successfully implemented a Custom IdentityUser.Like So
public partial class Authentication : IdentityUser
{
public Authentication()
{
this.LoginSessions = new List<LoginSession>();
}
[Required]
public string PersonId { get; set; }
public virtual Lecturer Lecturer { get; set; }
public virtual Student Student { get; set; }
public virtual ICollection<LoginSession> LoginSessions { get; set; }
}
with the following Maps
public class IdentityUserLoginConfiguration: EntityTypeConfiguration<IdentityUserLogin>
{
public IdentityUserLoginConfiguration()
{
HasKey(t => t.UserId);
}
}
public class IdentityRoleConfiguration : EntityTypeConfiguration<IdentityRole>
{
public IdentityRoleConfiguration()
{
HasKey(t => t.Id);
}
}
public class AuthenticationMap : EntityTypeConfiguration<Authentication>
{
public AuthenticationMap()
{
// Primary Key
this.HasKey(t => t.PersonId);
// Properties
this.Property(t => t.PersonId)
.IsRequired()
.HasMaxLength(14);
// Table & Column Mappings
this.ToTable("Authentication");
this.Property(t => t.PersonId).HasColumnName("PersonID");
// Relationships
this.HasOptional(t => t.Lecturer)
.WithOptionalPrincipal(t => t.Authentication);
this.HasOptional(t => t.Student)
.WithOptionalPrincipal(t => t.Authentication);
}
}
But now my problem is that when I'm adding a user to a Role Using the
UserManager.AddToRole()
method I get a DBValidationError
This is really worrying me and would like some help as soon as possible