Error to unauthorized access of file in C#

<pre> try
            {
                string path =Application.StartupPath + "\\OTS.exe.config";
                var doc = new XmlDocument();
                doc.Load(path);
                XmlNodeList endpoints = doc.GetElementsByTagName("connectionStrings");
                foreach (XmlNode item in endpoints)
                {
                    if (item.HasChildNodes)
                    {
                        foreach (var c in item.ChildNodes)
                        {
                            if (((XmlNode)c).NodeType == XmlNodeType.Element)
                            {
                                var adressAttribute = ((XmlNode)c).Attributes["name"];
                                if (adressAttribute.Value.Contains("OTSConnection"))
                                {
                                    ((XmlNode)c).Attributes["connectionString"].Value = connection_string;
                                    //((XmlNode)c).Attributes["providerName"].Value = SetupConstants.DbEmbededConnectionProvider;
                                }
                            }
                        }
                    }

                }
                doc.Save(path);    // it is not saving the file. jump to catch block.
                string exePath = Path.Combine(path,"OTS.exe");

                return true;
            }
            catch
            {

                return false;
            }