It sounds like you are taking every step possible to overcome some very common problems with network shares. The FileSystemWatcher and sleep(3000) may not be enough. Try creating a locked file (FileStream with Non-Sharing Mode) that your "listeners" try to access. Remove the lock once the message has been added and the excel file is written. But my guess is that you will never get rid of this problem. File access using network shares are never reliable when accessed from multiple computers simultaneously (in my experience).