THIS POST CONTAINS A TRIED AND TESTED SOLUTION FOR THIS PROBLEM.
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WHAT IS THE PROBLEM?
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Once Lion is installed, Keynote becomes incredibly sluggish, showing the beach ball of doom frequently and for many minutes at a time. This happens during rehearsal and presentation, too. This seems to happen in presentations that contain video. For some users, even 1 slide with video on it seems to cause the problem.
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WHY IS IT HAPPENING?
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There seems to be a bug in Versioning which is handling videos in Keynote badly. Versioning does saving in the background, and somehow it seems to all the wrong things in presentations with video.
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IS THERE A FIX FOR THIS PROBLEM?
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There is no official fix from Apple for this problem. There is an unofficial fix, which fuzzydog first suggested, which is to DOWNGRADE Keynote from version 9.1 to version 9.0.5. The difference between version 9.0.5 of Keynote and the version 9.1 of Keynote is Versioning, and that's basically it. So downgrading will get rid of Versioning, and fix this problem. INSTRUCTIONS ARE BELOW.
Some users have suggested several fixes which work for them but DID NOT WORK FOR ME and have not worked for other users, as well. These include:
1) I tried unchecking the "Back up previous version" checkbox in Keynote Preferences. While some people reported that this worked for them, it made no difference for me.
2) I tried unchecking the "Lock documents 2 weeks after last edit" item in Time Machine Options. This also did not work for me.
3) I tried duplicating the file and then opening it in Keynote. This would seem to work at first, then deteriorate. Why? My thought is that when you duplicate a file you get rid of it's "version history" that Lion and Keynote are using instead of save, but once you start actually going through the presentation it starts a new version history and has problems again. In theory if you don't change anything in the presentation it shoudn't happen, but this only helps if your goal is just presentation. I need Keynote to work so I can edit, too.
4) I tried locking the file. This did work, and is fine for when you need to rehearse and present, but useless when editing a presentation. And Keynote is just unusable while editing, so I don't consider it a fix.
5) Go back to Snow Leopard. You can certainly do this and it will fix the problem but YOU DON'T NEED TO. All you need to do is to go back to an older version of Keynote.
6) Go to Powerpoint. Well, that's certainly an option. But if you're ready to make that big a change, I would suggest trying to downgrade Keynote first.
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SO WHAT IS THE FIX?
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Downgrade to the previous version of Keynote and this problem WILL GO AWAY. Instructions below:
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WHAT ARE THE STEPS TO FIX THIS PROBLEM?
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1. Find your iWork 9 DVD. If you downloaded iWork from the App store and do not have a disk, then you will need to find a disk. I don't know of any way to download an older version of iWork from the App store. Try eBay, try a friend, try going to the Apple store.
If you really cannot get the iWork 9 DVD in your hands, then your best option is to go back to Snow Leopard. If you cannot figure out how to do that, go to an Apple store and ask for help. Take a printout of this message with you.
2. Remove iWork 9.1 using the script supplied by Yvan Koenig. Just deleting iWork is NOT enough - you need to clean up all the iWork files or this won't work. The script found on this server:
https://public.me.com/koenigyvan
Look in the folder called "For_iWork", then "iWork '09" and then download the file called "uninstall iWork '09.zip". When that has downloaded and opened, click RUN. Wait several minutes while it gets rid of iWork. While it's working the button will say "Stop" and when it's done the "Run" button will reappear.
The script does not remove your personal templates stored in your user/library/application support/iworks folder, so you don't have to worry about losing those.
2. Reinstall iWork 9 from your disk.
3. Next you'll want to update iWork to version 5.05. You can get this here. http://support.apple.com/downloads/#iwork.
There are FOUR update packages: 9.0.1, 9.0.3, 9.0.4 and 9.0.5. Download and install them one at a time, in order. Yes, I know these are version 9.0.1+ and we're upgrading to 5.05 - who knows what's with that. Just roll with it.
4. The first time you open any iWork app (Numbers, Keynote or Pages) it will ask you to upgrade to 9.1. DO NOT DO THIS and check the box indicating NOT to be reminded again.
EVERY time in the future that you do a software update it will offer to update iWork for you. Make sure that each time you DO NOT UPDATE iWork to version 9.1.
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I DID WHAT YOU SAID AND IT DIDN'T WORK
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If it did not work, check the version number on Keynote (go to Keynote > About Keynote). If it says version 5.1 then you didn't properly uninstall the old iWork. If it says version 5.0.5, then it should be working.
If it's not, then this fix didn't work for you and you should definitely post a message to this forum because you would be the first person it didn't work for.
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WHY HASN'T APPLE RESPONDED TO THIS PROBLEM?
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There's a lot of posts expressing outrage over this problem and wondering why Apple hasn't resolved it. I have no idea. I do know that Apple DOES NOT READ these forums, so if you are having this problem you NEED to give Apple feedback.
Visit the Keynote feedback page and provide information here:
http://www.apple.com/feedback/keynote.html
Or go to the Apple store and show a genius this entire post and have him register the problem. Or call Apple, if you've the patience.