In 64-bit versions of Mac OS 10.5 and later, some older, optional plug-ins are available only if Photoshop is running in 32-bit mode:
In the Finder, choose Go > Applications.
Expand the Photoshop folder. Then right-click the Photoshop application icon, and choose Get Info.
In the General section of the Info window, select Open In 32-bit Mode.
Close the Info window, and restart Photoshop.
For more information, see 64-bit operating system benefits and limitations
in Photoshop.