the installer can't open the package. There may be a problem with the file ownership or permissions.

This procedure will delete certain temporary and cache files used by system processes. The files are automatically generated and don't contain any of your data. Occasionally they can become corrupt and cause problems such as yours.

Back up all data and read this whole message before doing anything.

Triple-click anywhere in the line below on this page to select it:

/var/folders/zz

Right-click or control-click the highlighted line and select

Services ▹ Reveal in Finder (or just Reveal)

from the contextual menu.* A folder should open with a subfolder named "zz" selected. Move that subfolder to the Trash. You may be prompted for your administrator login password. Restart the computer and empty the Trash.

IMPORTANT: It's been reported a few times that a computer failed to restart after the zz folder was moved to the Trash. If that happens, it means that the operating system is corrupt (and was already corrupt before you moved the folder.) In that case, there's no need to panic. Just reinstall the OS. If the system was upgraded from an older version of OS X, you may need the Apple ID and password you used. If you installed the Java runtime distributed by Apple and still need it, you'll have to reinstall it. The same goes for Xcode. All other data, including all your documents and settings, will be preserved.

*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select

Go ▹ Go to Folder...

from the menu bar and paste into the box that opens by pressing command-V. You won't see what you pasted because a line break is included. Press return.

Launch the Console application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

Select

/var/log ▹ install.log

from the log list on the left. If you don't see that list, select

View ▹ Show Log List

from the menu bar at the top of the screen. The contents of the log will appear on the right. Each log message begins with a timestamp. Select the messages from the time of the last installation or update attempt. If you're not sure when that was, click the Clear Display button in the toolbar of the Console window and then try the installation again. Select the new messages that appear. Copy the messages to the Clipboard by pressing the key combination command-C. Paste into a reply to this message (command-V).

If there are runs of repeated messages, post only one example of each. Don’t post many repetitions of the same message.

When posting a log extract, be selective. Don't post more than is requested.

Please don't indiscriminately dump thousands of lines from the log into this discussion.

Please don't post screenshots of log messages—post the text.

Some private information, such as your name, may appear in the log. Anonymize before posting. You may need to use a text editor with search and replace, such as TextEdit.

When you post the log extract, you might see an error message on the web page: "You have included content in your post that is not permitted," or "The message contains invalid characters." That's a bug in the forum software. Please post the text on Pastebin, then post a link here to the page you created.

It's fairly common. I don't know what causes it.