Running MacBook Air, 10.9.4. iCal suddenly stopped connecting to Exchange. I deleted account settings, and re-created Exchange account in System Preferences > Internet Accounts. I received "There was an error in Internet Accounts preference pane.". Checked some discussion threads and saw that for some, disconnecting Internet access and manually setting server worked. I tried this, and was able to set-up Exchange account, however it works for everything except calendar (i.e., it syncs with notes, email etc). When I open iCal, my Exchange account appears as a calendar option in the left of iCal screen, but none of my calendar entries appear in the calendar part of the iCal screen.
All other account calendar entries (e.g., my Google Calendar) appear fine.
I reset again all the iCal prefs and caches ( (~/Library/Calendars, ~/Library/Preferences/com.apple.iCal.plist, ~/Library/Caches/com.apple.iCal) and RESTARTED the Mac. Then I opened iCal and added back the Exchange account, and all working good.