Flash Publishing - writing over older files?

Wondering if anyone can offer suggestions on what I’m missing. I create a wonderful flash file… with or without video. I publish the files and upload to the web. Everything works beautifully. However if ever I need to make changes (which is all the time) to the file, I go in and ‘publish’ again over the same files and upload to the net, I get a blank screne every single time. Before publishing, I test the movie and it appears to run wonderfully. I test the html file and it appears to run wonderfully. However when I upload to the net, I get ‘nothing’… nada… zippo… I end up having to save the .fla file under an entirely new name and upload… I would like to keep the same html page, but can’t… can anyone offer ideas on what may cause this? I’m running Flash 8 Pro and using Dreamweaver 8 to upload. Thanks ever so much!!