I understand that you are not able to install the plug in from Watch on Slingbox.com. This issue might be caused by the browser or system that you are using. First, make sure that your equipment meets the requirements and also try with another supported browser.
Once that's done, feel free to complete the following troubleshooting steps and let us know if the issue persists:
If you have the same issue, we recommend you to be as specific as possible with the details provided. This way, other forum users will be able to help you with accurate information.