I am sorry to hear that you are having issues viewing your Slingbox. When things aren't working the way that they should it is never a pleasant experience. I have attached a link below that I hope will be helpful in finding a resolution to the issue at hand.
Hope this helps,
Sling Moderation Team
Thank you, however the issue has now been resolved. Support centre interrogated my Slingbox through my computer. Basically needed a number of factory resets to clear the system. This involved holding down reset button for a full 30 seconds, not what is normally suggested. Eventually it cleared after about 6 attempts, to factory default and I could reset the system. Just in time, off to Africa on Monday.
Thank you customer support team!