Please try this code.....
DataRow dr = dtPrf_Mstr.NewRow();
dtPrf_Mstr.Rows.Add(dr);
GVGLCode.DataSource = dtPrf_Mstr;
GVGLCode.DataBind();
int iCount = GVGLCode.Rows.Count;
for (int i = 0; i < iCount; i++)
{
GVGLCode.Rows.Remove(GVGLCode.Rows[i]);
}
GVGLCode.DataBind();