I think the problem is in your server configuration. If you are using IIS server, then you have to add .flv MIME type in IIS. You can do so by following the steps below:
1. Select the site in IIS, right click and select Properties
2. Under HTTP Headers Tab, select "File Types" under the MIME Map section and select "New Type"
3. Type ".flv" as the associated extension and "video/x-flv" as the content type.
4. Select "OK" complete your set up.
Hope this will solve your problem.
