This sounds like to me that the Slingbox needs a hard reset performed. Have a look at this article below to complete a hard reset:
After the reset is done, you can then go back to newwatch.slingbox.com and set your unit back up again.
If this error still occurs after the hard reset, please contact Sling Media Technical Support at 1-877-GO-SLING (877-467-5464)
Hope this helps!!!
Sling Media Moderation Team