Lookup field not updating when the document uploading

Question

I am uploading document programically and passing lookup field value but its not get updated, how to handle this?

   using (var site = new SPSite("http://ussecavpdvrwk06/sites/TAS/"))
       {
           using (SPWeb web = site.OpenWeb())
                {
                    SPList sharedDocumentList = web.ServerRelativeUrl.Equals("/")
                              ? web.GetList(web.ServerRelativeUrl + "SharedDocuments")
                              : web.GetList(web.ServerRelativeUrl + "/" + "SharedDocuments");
                    Hashtable propertiesHash = new Hashtable
                        {
                            {"EYReverseLookupRelatedTasks", "3110112619"}//get_ID(web, "Lists/Tasks", "LinkTitle", "3110112619")}                                                 
                        }; 

                    byte[] strm = File.ReadAllBytes("C:\\xml\\XMLDATAFile.xml");
                    sharedDocumentList.RootFolder.Files.Add(sharedDocumentList.RootFolder.Url + "/" + "mydocxml", strm, propertiesHash, false);

                    web.AllowUnsafeUpdates = false;
                }
        }

Answer 1

For a lookup column you must provide the ID of the item you are referring to.

Thus if the item being lookup has an ID of 3 you must provide that in the hashtable, with lookups to multiple items you must provide the ID and the value separeted by ;# e.g.: 1;#First Item;#3;#THirdItem.

Answer 2

You need have to update the SPList object...