I met several problems as most people said here, finally, I figured them out.

first, you need disable Date, dateAPI, Calendar, Calendar iCal in administer/ modules.
second, the best way is that you need to backup your two folders Date and Calendar in somewhere, so if you meet problem just copy back. then delete these folders from sites/all/modules.
third, download and unzip Date-5.1-dev and calendar-5.1-dev to sites/all/modules, you must change these two modules at same time. do not just change one.
follow the http://drupal.org/node/133341 instruction to reinstall.
the events you created need to update(submit again I don't why. but for me, only after resubmit, it works).

Good luck.

Richard

Comments

KarenS’s picture

Status: Active » Fixed

Not an open issue. This is all mentioned already in the documentation, so I don't think it needs to be an open issue in the queue, but thanks for sharing.

Anonymous’s picture

Status: Fixed » Closed (fixed)