What does this Android build error mean?

Hi. I’m new to Android development and I keep getting this error when I try to create a development build. What does it mean and how can I fix it (if it’s relevant, I’m running Mac OS X Mavericks)? Thanks.

Error building Player: Win32Exception:

Hi, this error means your Android SDK installation is missing zipalign utility. It has been moved into another directory by Google in one of the recent updates. We have fixed Unity to handle this correctly in 4.5.2. If you are using an earlier version - probably it’s worth upgrading then.