Problema dandole formato a un decimal en c#

[ramirezmario7]

Hola intenta agregando este codigo.

using System.Threading;
using System.Globalization;


Thread thread = System.Threading.Thread.CurrentThread;

NumberFormatInfo numericFormat =
((NumberFormatInfo)CultureInfo.CurrentCulture.Numb erFormat.Clone());

CultureInfo culture = CultureInfo.CreateSpecificCulture("es-CO");

//Se configuran los formatos
numericFormat.NumberDecimalSeparator = ",";
numericFormat.CurrencyDecimalSeparator = ",";
numericFormat.NumberGroupSeparator = ".";
numericFormat.CurrencyGroupSeparator = ".";

//Se configura el Culture con los formatos anteriores
culture.NumberFormat = numericFormat;

//Se lleva al thread el Culture
thread.CurrentCulture = culture;

edito: falto agregar la linea
CultureInfo culture = CultureInfo.CreateSpecificCulture("es-CO");