Mac OS X 10.0: Num Lock Prevents Dragging in Cocoa Applications

If the Num Lock key is activated while using Mac OS X, you may be unable to drag or arrange items within Cocoa applications.
Symptom

An item can be selected within an application, such an email message in the Mail application, but you cannot drag or arrange it. This may also be seen in the language list in System Preferences, and potentially other lists in the system.


Note: Software developers may create applications for Mac OS X to run in environments that include Classic, Carbon, and Cocoa. This issue may only affect applications designed for Cocoa.

Solution

Turn off Num Lock. This is done by pressing the Num Lock key while pressing and holding the Shift key.
Published Date: Feb 17, 2012