Calendar & Clock don't work after installing BytaFont Design

I'm sure this response is a bit late and i apologize for that, but in my case with the same iPhone 4 with iOS 7 i had the same problem trying to install the same font, i assume that you got dbk1ng's or spydar007's version of the San Francisco font. There is no fix as this font is incompatible with this device, that's at least what other forums were saying, and the only alternative i could find for this, was to get App Icons from the app store, make a fake calendar app (just a redirection app) and change the lock screen font to the standard "Helvectia" font that comes with iOS stock. You can do this by going to the bytafont tweak mode. Doing this you loose out on the real time calendar icon, and you loose out on the San Francisco font on the lock screen, but everything else like the menu bar and apps will have the San Francisco font. I hope this helped and if you need more help please ask.