iOS 8.1.1 update on iPhone 4S, calendar not working now I cannot view my daily appointments or view pending calendar invites since I updated my iOS software to 8.1.1.
After almost 2 months I figured it out.  I set up the Gmail/Google Calendar/Google Contacts on my iPhone as an Exchange Account many years ago.  Google discontinued this in 2013 for all new users, though it still worked for me (until Nov 17th).  Google now uses CardDAV for Contacts and CaIDAV for Calendar (since 2013).  They recommend using the Gmail app for their mail.  Here is a link on how to set up Gmail/Contacts/Google Calendar: https://support.google.com/mail/answer/3008051?hl=en
I did this yesterday and now everything works.  I was surprised that there weren't more complaints about the issue (I thought there must be hundreds of thousands of people affected) but most people probably have it set up using the newer method, which obviously wasn't affected by iOS 8.1.1