Context trying to delete 2 times the same record

I'm having a problem, in fact it should be the lack of knowledge even at the time of deleting a record using Entity Framework 6.

When I try to delete a record that can not be deleted because it has references, it gives the following error:

Sofar,allright.

I'lltrytodeleteanotherrecord,whichI'msurehasnoreference,anditgivesthesameerror,it'sactuallytryingtodeletethepreviousrecordagain.

IfIleavethescreenandenteragainthenIcandeletetheregistrynormally,aslongasIdonottrytodeleteanotheronebeforeitgeneratestheerror.

Doesanyonehavealight?Vlw

EDIT:Here'smycodetobetterunderstand:

ScreenSignature:

privatereadonlyICategoriaAppService_categoriaApp;privateCategoriaViewModel_categoria;publicFormCategorias(ICategoriaAppServicecategoriaAppService){_categoriaApp=categoriaAppService;InitializeComponent();}

Methodtoexclude:

privatevoidbtnExcluir_Click(objectsender,EventArgse){DialogResultresposta=MessageBox.Show("Deseja excluir este registro?", "Excluir", MessageBoxButtons.YesNo, MessageBoxIcon.Question);
    switch (resposta)
    {
        case DialogResult.Yes:
            var categoriaDomain = _categoriaApp.ObtemPeloID(_categoria.Numero_Categoria);
            _categoriaApp.Excluir(categoriaDomain);
            MessageBox.Show("Registro excluido com sucesso");
            break;
        case DialogResult.No:
            break;
    }
}

AppService:

private readonly ICategoriaService _categoriaService;

public CategoriaAppService(ICategoriaService categoriaService) : base(categoriaService)
{
    _categoriaService = categoriaService;
}

public void Excluir(TEntity obj)
{
    _serviceBase.Remove(obj);
}

Service:

public class ServiceBase<TEntity> : IDisposable, IServiceBase<TEntity> where TEntity : class
{
    protected ControleEstoqueContexto Db = new ControleEstoqueContexto();

    public ServiceBase()
    {
        Db.Configuration.AutoDetectChangesEnabled = false;
    }

    public virtual void Remove(TEntity obj)
    {
        try
        {
            Db.Set<TEntity>().Remove(obj);
            Db.SaveChanges();
        }
        catch (Exception e)
        {
            Db.Dispose();
            Db = new ControleEstoqueContexto();
            throw e;
        }
    }

    //ETC
}

EDIT 2: Resolved by putting try catch and remapping Db.Context. Code changed above.