Windows XP is not currently a supported operating system. We currently support Windows 7 and newer or Mac 10.9.X or newer.
With that being said, you could still try a view things. Start with clearing the browsers cache/cookies. You could also uninstall the SlingPlayer plug-in then reinstall it. Here's some articles that should help:
- Which SlingPlayer software works with my Slingbox?
- Slingbox.com - Troubleshooting Watch on Slingbox.com installation or usage
- Slingbox.com - Installing/removing browser plug-in for Watch on Slingbox.com
Hope this helps!