I had this same problem and I found out how to fix it. What you need to do is go through all your mods and update everyone of them. (This means just deleting them and then downloading the newer version.) I did this with 5 mods and when I went back in the game, the calendar was fully functioning again, so try it. Good luck!
Hello
This issue was fixed in the patch today
It would be best to now update your game
Calendar events will now occur on the day for which you planned them, thus ending centuries of debate on the purpose of a calendar.
Player created events will now appear on the calendar as expected.
NOTE: As a result of some calendar improvements, the dates for some of your currently scheduled events
Comments
This issue was fixed in the patch today
It would be best to now update your game
http://forums.thesims.com/en_US/discussion/817478/hello-come-and-introduce-yourself
http://tinyurl.com/OneRoomOneWeek
http://tinyurl.com/rosemow
My Showcase thread https://forums.thesims.com/en_US/discussion/948861/rosemow-s-rooms-showcase