So recently around the office we started noticing that the calendars listed under “Other Calendars” in outlook would just disappear if you clicked on them.  This only happened to the calendars listed coming from Public Folder favorites.  This is what I did to fix the problem.

1. Go into your Public Folder Favorites and delete whatever favorites your previously created.
2. Close Outlook
3. Click on START and then RUN and enter %appdata%.  This will take you to the following directory:  C:\Users\<usernamehere>\AppData\Roaming
4. Inside the path above navigate to the Microsoft and then Outlook folder.
5. In the Outlook folder you will see a Outlook.xml.  Rename that file to something else.  (Add .old to the file name).  It is never a good idea to delete a file when troubleshooting an error.  Always try to rename the file causing the problem.  You can rename it back if this fix does not work.
6. Launch Outlook once you have completed step #5
7. Navigate to your Public Folders and add the Calendars back to your favorites.