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Duplicate Calendar Items in Sync-to-Sharepoint 2003 via Outlook 2007

I'm running Sharepoint 2003 with WSS 3.0, supporting two-way communication with Outlook 2007.  We're transitioning a handful of public calendars in exchange to the Sharepoint services; as there aren't many items in them, we're simply using list view and cutting-and-pasting via Outlook.

So far, it's pretty simple.


On several calendars, it just seems to rampantly duplicate the calendar items - in one memorable case, over eight times resulting in nearly eighteen thousand items in the calendar. I believe, but can't yet confirm, that it's happening each time my local client syncs with the calendars in question.

What's going on, and how can I stop this repeated item duplication?  It's making the calendars almost unusable, at this point.  Right now, i can still wipe them out and replace the entries - but only because my users are holding off using these services for a day or so as we sort out troubles.  
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1 Solution
Joanne M. OrzechManager, Document Services CenterCommented:
Just popping in since you haven't had a response, there are a few ideas here:


Check to see if you have more than one Outlook running. Having more than one Outlook process running while synchronizing can lead to duplicate appointments. To see if you have more than one running, quit Outlook, open the Task Manager and go to the processes tab. Once there, click once on the "Name" column to sort alphabetically, then look for "Outlook.exe". If it's listed there, then highlight it and click on "End Process". Some people report finding up to four copies of Outlook running using this method. You should be able to resume your synchronization after performing this step.

Duplicate appointments can also be created by accepting a meeting request in Outlook Web Access. See the Microsoft knowledge base article titled "A duplicate appointment item is created when a user accepts a meeting request in Outlook Web Access" for more information about this.

I think you're probably on the right track though that the syncing may be causing this....

JonahGrimmAuthor Commented:
Thanks, JO -

I resolved this issue, and here's what I found and the (somewhat esoteric) problem that was causing it.

We have (had) about thirty public calendars, ranging in size from ones barely used (20 entries) to some heavily used (2200 entries).  I isolated it to only the larger calendars duplicating.  To solve the issue in the short term, I deleted all of the new SharePoint calendars and tried resynching them again.

What I discovered was that Outlook syncs each calendar immediately upon completion, not during a regular sync cycle.  Further, starting a second calendar before the first had completed (that is, copying items while the other calendar is syncing into a new sharepoint calendar) causes BOTH unsynced calendars to start syncing.  Again.

So - you've got your original sync ongoing, then the new calendar forks another sync of that unfinished calendar, as well as a sync of the new calendar.

Small calendars that sync quickly weren't generally 'caught' in this loop - they were done before I could start the next calendar.  They would, however, cause the big calendars to loop one more time.

The resolution is simple:  do one calendar at a time, allowing it to complete fully before moving on to the next one.  I also found that it was useful and helpful to allow a calendar to sync, then disconnect from it on SharePoint to get it out of any potential update queue.  It also helps to ensure that your outlook is NOT automatically sending-and-receiving during this process, though that didn't cause duplicates, just slowed me down to a crawl.

So.  One calendar at a time.  Let it sync fully.  Disconnect it when you're done (to avoid potential loop problems).   Now that they're all up, I can sit and watch them, and I'm not spawning duplicate items.  

Very odd bug to find.
Joanne M. OrzechManager, Document Services CenterCommented:

Thanks so much for posting this solution.  I would have NEVER guessed that!  LOL

Hope your holidays are happy.


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