Scorch files won't play (sometimes)
 

I've created Scorch .htm files using Sibelius First. I've installed the Scorch Plugin in both IE and Firefox. When I open the Scorch files directly in a browser (i.e., double click on the files in Windows Explorer) everything works fine. However if I upload the htm files to a website, or even email them to myself and then click on the link, the webpage tells me that Scorch isn't installed (using the same browser that I used when I successfully opened the files). If I save the webpage source to a file and compare it to the one I uploaded it's identical. What am I doing wrong?

Thanks
Mike