We need you to be more specific. Unfortunately, your post is not clear enough and we need you to give us more information. Do you have this issue using the Desktop SlingPlayer or the Web Based application at Watch.slingbox.com?
If you are planning to connect to the Slingbox using the web based SlingPlayer, I recommend to check all the driver updates for Java, Flash Player and ActiveX, after that, you should be able to log in normally. Please have a look at this thread to confirm if that's the same behavior that you are getting