display names in new line .enviorment.newline

[pree123]

hi
I am writing this:

if (!countForChildSupplier.Equals(SysXConsts.NONE))
                {
                    errorMessage = "Please reject these supplier changes as listed child supplier(s) is/are already mapped with other supplier(s)." + Environment.NewLine;
                    duplicateChildSuppliers.ForEach(item =>
                        {
                            errorMessage = errorMessage + item + Environment.NewLine;
                        });
                    errorMessage = errorMessage.Substring(SysXConsts.NONE, errorMessage.Length - SysXConsts.ONE);
                    errorMessage = errorMessage + "." + Environment.NewLine;
                }

I want the names of the item in new line ,but it is not being displayed.