iPhoto crashes when creating a new slide show

Try the following:

1 - delete the iPhoto preference file, com.apple.iPhoto.plist, that resides in your

User/Home/Library/ Preferences folder.

2 - delete iPhoto's cache file, Cache.db, that is located in your

User/Home/Library/Caches/com.apple.iPhoto folder (Snow Leopard and Earlier).

or with Mt. Lion from the User/Library/Containers/com.apple.iPhoto/
Data/Library/Caches/com.apple.iPhoto folder

3 - launch iPhoto and try again.

NOTE 1: If you're moved your library from its default location in your Home/Pictures folder you will have to point iPhoto to its new location when you next open iPhoto by holding down the Option key when launching iPhoto. You'll also have to reset the iPhoto's various preferences.

NOTE 2: In Lion and Mountain Lion the Library folder is now invisible. To make it permanently visible enter the following in the Terminal application window: chflags nohidden ~/Library and hit the Enter button - 10.7: Un-hide the User Library folder.

OT

How much free space do you have on your boot drive? Try this: launch iPhoto with the Option key held down and create a new, test library. Import some photos and test to see if the same problem persists.

Are you running a "Referenced" library?

If so and the photos are on the NAS that's probably the cause. Running a Referenced library is definitely not recommended and iPhoto is known to have problem with NAS servers.

Log into another user account on your Mac and see if you can run iPhoto and create a slideshow successfully and easily from there.

It looks like there's something in your account that's the culprit. It could be a preference file other than iPhoto's. Here's how to test that:

Trouble Shooting Preferences

NOTE: In Lion and Mountain Lion the Library folder is now invisible. To make it permanently visible enter the following in the Terminal application window: chflags nohidden ~/Library and hit the Enter button - 10.7: Un-hide the User Library folder.

1 - close all applications.

2 - open your Home/Library folder and Option-drag (copy) the Preferences folder to the Desktop.

3 - select the contents of your Home/Library/Preferences folder and drag them into the Trash bin in the Dock. You will be asked to provide your Admin password.

4 - reboot.

5 - run the application again and determine if the problems is fixed

6 - If the problem is fixed:

A - open the working Home/Library/Preferences folder.

B - Open the Preferences folder on the Desktop, select all of the contents and drag them into the working Home/Library/Preferences folder.

C - When the Copy window pops up check the "Apply to All" check box and then click on the Don't Replace or Skip button.

D - reboot.

7 - If the problem is NOT fixed, drag the contents of the Preference folder on the Desktop into the Home/Library/Preference folder and replace the entire contents that were created by clicking on Replace.

8 - reboot.

Disconnect the NAS and see does the problem recur?

Or maybe it helps when I export the iPhoto library to the NAS?

That won't help. You can't do it. iPhoto needs to have the Library sitting on disk formatted Mac OS Extended (Journaled). Users with the Library sitting on disks otherwise formatted regularly report issues including, but not limited to, importing, saving edits and sharing the photos.

What version of iPhoto are you using? Launch Activity Monitor and watch the CPU column for the most active item when you launch iPhoto with the WiFi connected. That might indicate which is taking up the time. Also launch the Console app and check the reports for the time of the launch.

Doesn't really speak to me either. There's something about the NAS connected to the Mac that is interferring with iPhoto's operation. Go to the Mt. Lion forum and ask there about NAS -Mac-iPhoto.