Hi Member 12784611,
I was waiting for your reply. So I am writing on my guess as posted in the above comment.
As long as I know you need to do the formatting before binding, and perhaps after binding the format cannot be changed. Since I don't have your code I geared up a little code as follows:
DataTable DT = new DataTable();
DataColumn DC = new DataColumn();
DC.ColumnName = "Val";
DataRow DR = DT.NewRow();
double Dbl = 10000000000L;
DR["Val"] = Dbl.ToString("0,000");
textBox1.DataBindings.Add("Text", DT, "Val");
Please have some idea from here and modify your code accordingly.