Q: iPhoto doesn't rebuild thumbnails

Welcome to Apple Discussions,

Sounds like you might have a permissions issue with your iPhoto Library.

To try and resolve your issue:

Ensure all your software is up to date (Apple Menu > Software Update).

Remove the following to the trash and restart the computer and try again:
Home > Library > Caches (I remove the whole folder. It will be re-generated upon restart.)
Home > Library > Preferences > com.apple.iPhoto (There may be more than one. Remove them all.)

If the issue persists try rebuilding your iPhoto Library following this article http://support.apple.com/kb/HT2638. Use the bottom 3 rebuild options.

Once the rebuild is complete, do another rebuild, this time checking off the 2 thumbnail rebuild options.

Hope that helps.

Where is the Library? On your start up disk? On another disk? If on another disk what format is it?

Regards

TD

Try rebuilding the Thumbnails again - in my experience that can take two or three goes to work.
Regards

TD

Are you running File Vault?
__This can cause interesting issues with files and file permissions. If you have it turned on, consider backing up your computer and turning File Vault off.

How much available space do you have on your hard drive?
--Click on the Finder icon (little blue on blue smiley face in the dock) and look at the bottom of the windows that appears. If your available space is less than 10 GB this can impact performance on the computer (I like 20 GB free myself).
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If doing several thumbnail rebuilds as TD suggests does not resolve the issue you can try manually rebuilding the thumbnails.
__NOTE: Make sure you have a back up of your iPhoto Library before you do this as it requires modifying the contents of the iPhoto Library which can cause permanent damage to the Library if done incorrectly.

Manually rebuilding the thumbnails in iPhoto:
__Quit iPhoto if it is open
__Right click or ctrl click on the iPhoto Library in question.
__Choose Show Package contents
__Remove the following files to the trash:
_Data
_Data.noindex
_Thumb64Segment.data
_ThumbJPGSegment.data
__Launch iPhoto while hold down command and option on the keyboard
__Choose the top 2 options rebuild all thumbnails

Were you running File Vault?

sorry if i'm being dense, but i can't find any of the 4 files mentioned, after selecting "view package contents." should they be in the root folder? thank you!

Did you look inside the iPhoto Library package or the application package? The library package will be located in your Pictures folder unless you've moved to it another location.