Thanks for using the forums. Sorry to hear you are having issues with the plug in. If you are getting this error, generally clearing the cache and cookies on your browser or uninstalling and reinstalling the app will fix the issue. Below please find articles for further help with this issue.
- How do I install the Watch on Slingbox.com plug-in? How do I remove it?
- What browsers and systems are supported by Watch on Slingbox.com?
The Sling Moderation Team