应用程序启动时的C＃Windows窗体应用程序更新

My application has been successfully updating for ages, and I've been making changes, releasing new builds etc every day for the past few months, but now, when the application starts (it checks for updates on startup), it begins downloading the updated version from the server, and then fails 3-quarters of the way through with the following message:My application has been successfully updating f