Here is something to try.
Go to newwatch.slingbox.com from a computer (Windows or Mac) and wait until the video is playing. Once the video is playing Select the words "Settings" at the top of the screen and then select "Configure Inputs".
After this, reset the inputs listed and then re-setup the Slingbox.
After this is done, make sure you are completely logged out of the SlingPlayer for iPhone application and then log back in. This should give your guide information back.
If you are still confused on this process, have a look at the following article:
Even though you have not changed your cable box, this articles then steps I indicated for your Slingbox 500.
Hope this helps!!
Sling Media Moderation Team