It sounds like you may have selected the wrong choice when selecting your cable provider during the setup of your Slingbox. It sounds like you ran into the situation where you had two choices for cable provider: Comcast - Cable, and Comcast - Digital (non-rebuild), or something to that effect (using Comcast only as an example here).
I see in your account that you have a Slingbox M1. What you want to do in this case is reconfigure the video input, and select the correct cable provider. Here is the process to do this:
1) Connect to your Slingbox on a computer using the Slingplayer for Desktop app.
2) Go to Standard View (so that the Guide and Settings tabs show up in the lower right).
3) Go to the Settings tab and click on "Reconfigure Video Input"
4) Click "Change Device"
5) Run through the process, and select the Digital option for your cable provider. Once done, your Guide should be fixed.
Hope this helps!