Cannot access a closed file error on adding a file to a library

I am trying to copy the attachments from a list to a document library. When I try to write into a document library, occasionally I am getting following error "The remote server returned an error: (500) Internal Server Error.  Cannot access a closed file.  Cannot access a closed file.  "

Any ideas on what is causing the problem. The code is specified below, The error message is specified after the code. Can you please let me know if I am missing anything. I cant find anything wrong in the code or in the library. The code is running as WCF Service and the call to process this is made from Infopath form.

            try
            {

                SPSecurity.RunWithElevatedPrivileges(delegate()
                {

 string siteURL = "Site URL";
                    using (SPSite site = new SPSite(siteURL))
                    {
                        SPWeb oWeb = site.OpenWeb();
                        SPList oList = oWeb.Lists["List Name"];
                        SPList docDestination = oWeb.Lists["Destination Library on same site"];
                        SPFolder fldRoot = oWeb.Folders["Destination Library on same site"];
                        SPFileCollection flColl = null;
                        SPQuery oQuery = new SPQuery();
                        oQuery.Query = "<Where><Eq>" + "<FieldRef Name=\"ID\"/><Value Type=\"Number\">" + RequestID + "</Value></Eq></Where>";
                        SPListItemCollection oItems = oList.GetItems(oQuery);

                        foreach (SPListItem lstItem in oItems)
                        {
                            if (lstItem["ID"].ToString() == RequestID)
                            {
                                if (lstItem.Attachments != null && lstItem.Attachments.Count > 0)
                                {
                                    foreach (String strName in lstItem.Attachments)
                                    {
                                        flColl = fldRoot.Files;
                                        SPListItem listtem = docDestination.Items.Add();
                                        SPFile FileCopy = lstItem.ParentList.ParentWeb.GetFile(lstItem.Attachments.UrlPrefix + strName);
                                        SPQuery oQueryDest = new SPQuery();
                                        oQueryDest.Query = "<Where><Eq>" + "<FieldRef Name=\"Name\"/><Value Type=\"Text\">" + FileCopy.Name + "</Value></Eq></Where>";
                                        SPListItemCollection collListItems = docDestination.GetItems(oQuery);
                                        string destFile = flColl.Folder.Url + "/" + FileCopy.Name ;
                                        if (collListItems.Count > 0)
                                        {
                                            String strFileNamePrfix = FileCopy.Name.Substring(0, FileCopy.Name.Length - 3);
                                            strFileNamePrfix = strFileNamePrfix + "_" + collListItems.Count.ToString();
                                            strFileNamePrfix = strFileNamePrfix + FileCopy.Name.Substring(FileCopy.Name.Length - 3,3);
                                            destFile  = flColl.Folder.Url + "/" + strFileNamePrfix;
                                        }
                                        byte[] fileData = FileCopy.OpenBinary();
                                        Trace.WriteLine("Board Services dest file" + destFile + " Count = " + collListItems.Count.ToString());
                                        SPFile flAdded = flColl.Add(destFile, fileData,true);
                                        SPListItem item = flAdded.Item;
                                        flAdded.Item.Update();
}

                                }
                            }
                        }
                    }
                });
            }
            catch (Exception ex)
            {

                string strLogEntry = ex.Message.ToString() + ex.StackTrace.ToString();
            }
            finally
            {
            }

Form submission failed. (User: xxxxx, Form Name: Template, IP: , Request: http://Site Url/Lists/List name/Task/editifs.aspx?List=e6647e38-cb01-46b3-8bee-308357045532&ID=116&Source=http://Site URL/Lists/List Name/AllItems.aspx?View={CB9F3C2B-49DF-4D75-9720-1E7E000FD229}&FilterField1=Status&FilterValue1=Completed&IsDlg=1&Web=706d51c9-e509-40f3-884a-7d40e126ff14, Form ID: urn:schemas-microsoft-com:office:infopath:list:-AutoGen-2013-12-06T16:11:54:747Z, Type: DataAdapterException, Exception Message: The remote server returned an error: (500) Internal Server Error.  Cannot access a closed file.  Cannot access a closed file.  
 at System.IO.FileStream.Write(Byte[] array, Int32 offset, Int32 count)    
The remote server returned an error: (500) Internal Server Error.)