**EDIT**
I've
finally gotten around to adding instructions for DM6. Had to delete some of the DM5 images however, but added links to the images I deleted. Skip the DM6 instructions if you're still rockin' DM5 (scroll down).
Enjoy!
DM6 Instructions:
4. With that part complete, plug your Storm into your pc and open Desktop Manager (from this point forward, referred to as "DM"). Once you have it open and your Storm is connected, click on the
Back up now button (Always a good idea anyway). Normally, DM will automatically do this when it is started. Making another backup will do no harm

.
5. Once the back-up process is complete. Click on the
Device drop-down menu, then select
Delete data...
6. Choose the
Selected Data selection, which will reveal the full list of data that can be deleted. Scroll down until ya find the
Calendar entry and tick it. You'll notice in the image below, I've also selected the
Calendar - All entry as well. This is really not necessary, but if it makes ya more comfortable then go right ahead

.
Now, if you wish to make another back-up that will only include this data you're about to delete, this is the time to make that choice.
When you're finished here, click on the
Delete button.
7. Once DM has done it's thing, let's go ahead and restore the Calendar DB.
Once again, click on the
Device drop-down menu. This time selecting
Restore...
8. The most recent back-up files should be listed at the top of the displayed list. Either select the back-up file you just made when deleting the Calendar DB or the full back-up file we created in the beginning (step 4).
Ensure to choose
Select device data and settings in the middle of the screen. Followed by choosing the
Calendar data. Note that when I deleted the DB's, I choose two sets of data to back-up. Only one is shown here, since that is all that DM happened to back up. This isn't a great pic to use as an example to rid duplicate entries, but since it's the only one I have. Just be sure to choose a recent back-up that has a
Calendar DB with
half as many entries as the
Calendar - All DB, and select that
Calendar data.
When you've completed ticking the correct selections, click on that
Restore button.
Skip down to step 9 below... DM5 Instructions:4. With that part complete, plug your Storm into your pc and open Desktop Manager (from this point forward, referred to as "DM"). Once you have it open and your Storm is connected, click on Backup and Restore
http://img.photobucket.com/albums/v6...r/07DMHome.png
5. Now select Advanced. After clicking the button, DM will load your databases from your Storm, this may take a minute or two.
http://img.photobucket.com/albums/v6...AdvOptions.png
6. In the right column, scroll down until you find the Calendar databases. Select Calendar (as shown in first image below) then click the << button in between the two database columns (shown in second image below).
Note: The Calendar - All database will show twice as many entries than the Calendar database, unlike what is shown below
.
http://img.photobucket.com/albums/v6...ar/09DMCal.png
http://img.photobucket.com/albums/v6...r/10DMCopy.png
7. When DM is done copying your calendar, select Calendar - All in the right column and click the Clear button.
http://img.photobucket.com/albums/v6...1DMCal-All.png
http://img.photobucket.com/albums/v6...DMCalClear.png
8. Once DM is finished, highlight your Calendar copy in the left column and copy it back to your Storm by clicking the >> button in the middle.
http://img.photobucket.com/albums/v6...DMCopyBack.png
9. That's it! You've successfully rid your self of the duplicate calendar entries
*Edit* ~ Here's a tip that may help quite a few that might have calendar entries entered in multiple calendars but
not duplicates. Open the Calendar -> BB Button -> Options -> in landscape view, bring up the keyboard and type "move". It will ask ya if you want to move all entries into the default calendar, click "Yes". Reboot (batt pull).