iOS 6.1/MS Exchange bug fix in the works
February 14th 2013
A bug with iOS 6.1 is causing havoc in enterprise environments. Released a couple weeks ago, a new bug was introduced with iOS 6.1 causes excessive server load when responding certain recurring calendar events on a Microsoft Exchange account. The bug specifically deals with a modification of a single appointment from a repeating event.
Apple says a fix will be available in an upcoming iOS update, but doesn't provide details of what that may occur. In the mean time, Apple suggests users can try turning the calendar sync off, wait, then turn it back on it to clear the problem.
Apple Support