Error building 32-bit OS X app?

Question

I'm working on my first Mac OS X app. My project was set-up with XCode defaults and I haven't touched any Build Settings. When building for Mac 64-bit, the app runs fine. However, when building for Mac 32-bit, I get a seemingly arbitrary error that says:

Semantic issue: Synthesized property 'myProperty' must either be named the same as a compatible ivar or must explicitly name an ivar.

What kind of things can I check for?