A number of people have found the use of some multi-touch gestures on their MacBook and MacBook Pro computers have stopped working. While two finger gestures such as pinch and scroll may still work, those that use three and four fingers may not anymore. Additionally, others have had instances where the computer refuses input of any kind.
If you're experiencing this problem, try the following suggestions to tackle the problem:
Run a permissions fix
Using Disk Utility to run a permissions fix on the boot drive has helped a number of people with this problem, so that would be the first route to take. Launch Disk Utility, select your drive, and in the "First Aid" section click the "Repair Disk Permissions" button.
reapply latest "combo" updater
If there is a problem with one or more system files that cannot be addressed with a permissions fix, refreshing all the changed files with the latest "combo" system updater should replace any faulty ones. The latest combo updater for Snow Leopard is available here.
reset PRAM and try with bluetooth disabled
This problem seems to be related to an input device problem, so try resetting the PRAM (hold options-command-P-R at boot until the system resets a few times, and then allow it to boot normally) and also disable bluetooth.
Error Enqueuing Memory Problem
The gestures and other input problems may also be coupled with the system log getting filled with the following error message:
/usr/libexec/hidd27: IOHIDEventQueueEnqueue: Error enqueuing memory. (0xe00002e8)
This error, noted in this Apple Discussion thread, has to do with the Human Interface Devices (HID) Daemon, which is responsible for handling shared resources for keyboards, mice, webcams, tablets, and other input devices over various interfaces including USB, Firewire, and Bluetooth.
The error appears to be a bug in Snow Leopard, and hopefully will be addressed by Apple soon. However, when it is happening people may not be able to provide various input to the system. Sometimes this is a small inconvenience such as the lack of multi-touch gestures, but also could be a complete lack of input support.
When this happens, most of the time people have hard-reset the system, though if you have Remote Login or Screen Sharing enabled (suggested troubleshooting services), then you should still be able to access the system and either restart it or try to kill the "hidd" process.
To kill the "hidd" process (it should be relaunched automatically), log into the system with a second Mac using either SSH or screen sharing, and with a terminal shell open run the following command:
sudo killall hidd