Cannot scroll in Preview or Safari with Trackpad on Yosemite

System Preferences > Trackpad > Scroll & Zoom

Uncheck Boxes beside all those 4 items and recheck those.

Best.

Please read this whole message before doing anything.

This procedure is a test, not a solution. Don’t be disappointed when you find that nothing has changed after you complete it.

Step 1

The purpose of this step is to determine whether the problem is localized to your user account.

Enable guest logins* and log in as Guest. Don't use the Safari-only “Guest User” login created by “Find My Mac.”

While logged in as Guest, you won’t have access to any of your documents or settings. Applications will behave as if you were running them for the first time. Don’t be alarmed by this behavior; it’s normal. If you need any passwords or other personal data in order to complete the test, memorize, print, or write them down before you begin.

Test while logged in as Guest. Same problem?

After testing, log out of the guest account and, in your own account, disable it if you wish. Any files you created in the guest account will be deleted automatically when you log out of it.

*Note: If you’ve activated “Find My Mac” or FileVault, then you can’t enable the Guest account. The “Guest User” login created by “Find My Mac” is not the same. Create a new account in which to test, and delete it, including its home folder, after testing.

Step 2

The purpose of this step is to determine whether the problem is caused by third-party system modifications that load automatically at startup or login, by a peripheral device, by a font conflict, or by corruption of the file system or of certain system caches.

Please take this step regardless of the results of Step 1.

Disconnect all wired peripherals except those needed for the test, and remove all aftermarket expansion cards, if applicable. Start up in safe mode and log in to the account with the problem. You must hold down the shift key twice: once when you turn on the computer, and again when you log in.

Note: If FileVault is enabled in OS X 10.9 or earlier, or if a firmware password is set, or if the startup volume is a software RAID, you can’t do this. Ask for further instructions.

Safe mode is much slower to start up and run than normal, with limited graphics performance, and some things won’t work at all, including sound output and Wi-Fi on certain models. The next normal startup may also be somewhat slow.

The login screen appears even if you usually log in automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.

Test while in safe mode. Same problem?

After testing, restart as usual (not in safe mode) and verify that you still have the problem. Post the results of Steps 1 and 2.

I had MacBook Pro 17" late 2011, I upgrade yesterday to 10.10 and everything looks fine until today while I was browsing the web, updating my Adobe CS6 and uploading a medium size file via wetransfer.com. Then suddenly my trackpad stops scrolling on Safari 8.0 then I was almost going crazy, then I check that all other apps recognize Trackpad Scrolling and this was positive, Yesterday on late night I review ALL the new features on SystemPrefs and make some minor adjustments, and obviously I know by memory all my personalized SytemPrefs and my most used App new Prefs (Safari included).

Anyway wen this happens I rechecked all the trackpad prefs and nothing happens.

The next thing I thought was to close my user session, and start any other user (admin or standard, it doesn't matter) but I thought that this was not the solution in the moment.

I wait until my wetransfer.com upload and my Adobe updating finished, and then everything backs to normal like magic.

I will wait until I got a second or even a third time with this problem to make a full report.

I agree with Linc Davis to restart in "Safe Mode" to force the system to ignore any previous System Prefs. in order to create new ones automatically, if the problem persist verify which Apps are affected and what were you doing at the time to track the possible failures.

Greetings.

Sorry guys, barely a couple of minutes after i reply my Safari went wild again when the "System Notifications" appear my Safari stops scrolling nor reacting any multitouch feature (like forward/backward between pages navigation).

I notice that this time all multitouch features did affect the system (not mission control, nor notifications bar, App exposé, etc) but scrolling was active on mail, Chrome, Firefox, Calendar and any other App previously or post opened.

I'm gonna try system restart, and if persist use the "Safe Mode" option.

greetings.