Mighty Mouse 'center button' and 'squeeze button' not working

Go to System Preferences Mouse pane, and even if the settings for the squeeze and center-click are set as desired, change it to something else. Check if that setting is recognized. If it is, change it back to see if the original settings are now recognized.

If that does not work, be sure to run Disk Utility and use +Repair Disk Permissions+. Also reset PRAM

http://support.apple.com/kb/HT1379

then reset SMC

http://support.apple.com/kb/HT1543

which is basically disconnecting ALL cables and power, then reconnecting using a precise procedure. Initially power up with nothing connected, except power cord. Leave all peripherals (USB/FireWire) disconnected. Then only pair your wireless mouse. The Bluetooth receiver is on a USB bus, so try it initially with nothing else connected. If that works, connect your other peripheral devices one by one and note if the problem recurs. If the problem does recur at some point, try to identify if one of the other devices is interfering with the mouse.

If the problem recurs even with nothing connected except for the wireless mouse, try this test. Connect your keyboard and create a new admin user account in System Preferences Accounts pane

http://docs.info.apple.com/article.html?path=Mac/10.6/en/8235.html

Log out and log in to the new account. Does this problem recur in the new user account? If it does not, the cause is probably something in your normal account. If it does recur, even in the new account, the cause is probably something at the system level. Normally, it might also be hardware-related, but since this is the second mouse, it probably is not (unless there is some odd issue with the Bluetooth receiver).

If the problem recurs in more than one user account (including a brand new user account), then the problem is at the system level or hardware-related. It seems unlikely that two wireless mice would have the same physical problem, but it's certainly not impossible.

For software, you may have something installed as an extension that is interfering with operation of the Apple mouse. This could something like a third-party device driver. These are usually located at

<startup disk>/System/Library/Extensions/

so you may want to look through that folder for anything suspicious, such as a custom driver for a third-party mouse or some other input device.

Otherwise, if you have an external drive that you can erase, you can install a test system on it and set your iMac to start up from it. Then test your mouse using a fresh system installation. You can do this using your internal drive, but you would first have to back up at least your personal files, then erase and reinstall the system.

Third-party device driver... 🙂 Glad to hear it was something simple.