System.IO.IOException: The process cannot access the file 'file_name'

System.IO.File.Copy(path, ConfigurationManager.AppSettings["BulkInsertGiftRegisterCreatorDirectory"] + System.IO.Path.GetFileName(path));

Loyalty.Entity.Base.FileInfo file = new Loyalty.Entity.Base.FileInfo();
file.FileName = path;
request.Object = file;

ResponseBase response = new ResponseBase(request);
RequestConnection connection = new RequestConnection("cn");
FileManager fileManager = new FileManager(request, connection);
response = fileManager.OfflineGiftRegisterBulkInsert();

System.IO.File.Delete(ConfigurationManager.AppSettings["BulkInsertGiftRegisterCreatorDirectory"] + System.IO.Path.GetFileName(path));

// here is the part of stored procedure that uses file
SELECT @SCRIPT= 'BULK INSERT GIFT_CARD.GIFT_TEMP'
                            +' FROM '''
                            + @FILE_PATH
                            +''' WITH ('
                                 +'FIELDTERMINATOR = '','','
                                 + 'KEEPNULLS'
                            +');'

public static System.Boolean FileInUse(System.String file)
{
    try
    {
        if (!System.IO.File.Exists(file)) // The path might also be invalid.
        {
            return false;
        }

        using (System.IO.FileStream stream = new System.IO.FileStream(file, System.IO.FileMode.Open))
        {
            return false;
        }
    }
    catch
    {
        return true;
    }
}

public static void WaitForFile(System.String file)
{
    // While the file is in use...
    while (FileInUse(file)) ; // Do nothing.
}