After updating to OS X 10.6.4, a number of people are experiencing an error where Apple's Mail email client will not open. When the application is launched, a message stating "Mail version 4.3 (1081/1078) cannot be used on Mac OS X Version 10.6.4" is displayed and the program shuts down.
The version of Mail that is included with OS X 10.6.4 is 4.3 or build 1081, which can be found by right-clicking the Mail application, choosing "Show Package Contents", opening the /Contents/version.plist file, and checking the version string. Apple purposefully prevents some builds of Applications from running on different versions of OS X, and this type of error will be presented if you try to do so.
One reason this may happen if the OS X update did not complete properly and the system detects the version of Mail as being the older one. There are a few approaches you can try to fix the problem.
Reapply the combo updater
If this problem happens to you, the first thing to try is to reinstall the OS X 10.6.4 update using the "Combo" updater. Download the updater, boot into Safe Mode by restarting and holding the Shift key at bootup, and then run the installer. As an extra safeguard, you can runbeforehand to ensure permissions and caches are in order.
The OS X 10.6.4 Combo updater can be found here: http://support.apple.com/kb/DL1048
Downgrade Mail and then reapply the combo updater
Since the Combo updater may not have a full version of Mail included, and instead may only have updated components for Mail, you can try putting a previous version of Mail on the system and then running the combo updater to update it to the latest version. Older versions of Mail can be found in the following locations:
- A Time Machine backup
- On the Snow Leopard installation DVD (use Pacifist to extract it)
- From another computer running OS X 10.6.3 or earlier
Copy from another system
Lastly, if you have access to another system that has a properly functioning version of Mail, you can copy the program from that computer to your OS X 10.6.4 installation. You can use a USB flash drive or copy the program over the network and replace the one on your system, but after doing so be sure to run a permissions fix on the boot drive.
Archive and Install
As a last resort, if the update did not work you can either restore your whole system to a previous version by using Time Machine and then upgrading again with the "Combo" updater, or you can use the OS X 10.6 installation DVD to reinstall OS X. By default the installer will run an "Archive and Install" method, which will replace your system components and Apple-supplied applications with those that are on the DVD. From here, immediately update the system again using the "Combo" updater.