Why is The navigation property '' declared on type '' has been configured with conflicting multiplicities. error show up?

I've got anAsp_Users a table andResource tables. I have a question related to Entity Framework.Asp_Users POC and anResource POCO. Furthermore, theResource As a component of the Table-per-Hierarchy paradigm, POCO is abstract. The abstract in the Table-per-Hierarchy modelResource POCO and manyConcrete POCOs enjoyILCResource APO andSectionResource POCO. A one-to-many (1 to 0*) relationship exists betweenAsp_Users ONE-SIDED POCO TOResource POCO (many-side).

The pertinent portion of my aspnet Users POCO is as follows:

public partial class aspnet_Users
{
    public aspnet_Users() { }

    public virtual System.Guid ApplicationId { get; set; }
    public virtual System.Guid UserId { get; set; }
    public virtual string UserName { get; set; }
    public virtual string LoweredUserName { get; set; }
    public virtual string MobileAlias { get; set; }
    public virtual bool IsAnonymous { get; set; }
    public virtual System.DateTime LastActivityDate { get; set; }

    public virtual ICollection<Resource> associatedResources { get; set; }
}

Here is my Asp Users mapping settings.

public class Aspnet_UsersMap : EntityTypeConfiguration<PerlsData.Domain.aspnet_Users>
{
    public Aspnet_UsersMap()
    {
        this.ToTable("aspnet_Users", schemaName: "dbo");

        this.HasKey(u => u.UserId);

        this.Property(u => u.UserId)
            .HasColumnName("UserId")
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
        this.HasOptional(u => u.associatedResources);
    }
} 

The pertinent portion of my abstract Resource POCO class is as follows:

public abstract class Resource
{   
    public Resource(){
       // associatedPerspectives = new HashSet<Perspective>();
    }

    public virtual System.Guid ResourceDatabaseID { get; set; }
    public virtual string ResourceName { get; set; }
    public virtual string DescriptionOfResource { get; set; }
    public virtual System.Guid UserId { get; set; }
    public virtual Nullable<System.Guid> DepartmentDatabaseID { get; set; }
    public virtual string ResourceStatus { get; set; }
    public virtual Nullable<short> isRemoved { get; set; }

    public virtual Department Department { get; set; }

    public virtual System.Guid UserId { get; set; }
    public virtual aspnet_Users aspnet_Users { get; set; }


    public virtual ICollection<ResourceOverToILCResourcesBridge> associatedResourceOverToILCResourcesBridgeEntry { get; set; }
}

Here is my resource mapping configuration:

public class ResourceMap : EntityTypeConfiguration<Resource>
{

    public ResourceMap()
    {
        this.ToTable("Resources", schemaName: "dbo");

        this.Property(r => r.ResourceDatabaseID)
            .HasColumnName("ResourceDatabaseID");

        this.HasKey(r => r.ResourceDatabaseID);

        this.Property(x => x.ResourceDatabaseID)
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
        // .StoreGeneratedPattern = StoreGeneratedPattern.Identity;
        this.Property(r => r.ResourceName)
            .HasColumnName("ResourceName");

        this.Map<PerlsData.Domain.OtherItem>(m => m.Requires("discriminator").HasValue("otheritems"))
        .Map<PerlsData.Domain.Audioitem>(m => m.Requires("discriminator").HasValue("audioitems"))
        .Map<PerlsData.Domain.Imageitem>(m => m.Requires("discriminator").HasValue("imageitems"))
        .Map<PerlsData.Domain.Videoitem>(m => m.Requires("discriminator").HasValue("videoitems"))
        .Map<PerlsData.Domain.UriItem>(m => m.Requires("discriminator").HasValue("uriitems"))
        .Map<PerlsData.Domain.Documentitem>(m => m.Requires("discriminator").HasValue("documentitems"))
        .Map<PerlsData.Domain.DatabaseFileItem>(m => m.Requires("discriminator").HasValue("databasefileitems"));

        this.HasOptional(res => res.associatedResourceOverToILCResourcesBridgeEntry);

        this.HasRequired(res => res.aspnet_Users)
            .WithMany(u => u.associatedResources)
            .HasForeignKey(res => res.UserId);
    }
}

Please let me know why I'm seeing the following error.

The navigation property 'associatedResources' declared on type 'PerlsData.Domain.aspnet_Users' has been configured with conflicting multiplicities.

Please elucidate the reason why it remains NULL after my creation of the mapping in the POCO class.