OS X Yosemite may occasionally cause some programs to crash when you open, save-as, or first save a file. These crashes are rare but happen when an application, such as Dropbox, uses Yosemite’s official Finder integration — and if that program crashes because of this interaction, unsaved changes may be lost.
To fix this issue, Apple has released OS X Update 10.10.1. This update is available for free in the Mac App Store. Details on how to update your Mac are available on Apple’s support site.