Omnisphere plugin fails to scan

After installing Omnisphere on my MacBook Air, I start Synfire, and it reports that it failed to scan Omnisphere's VST3 plugin. I tried a few more times via Audi/MIDI Setup's "Scan Installed Plug-Ins," but it keeps failing. Omnisphere's standalone works fine. Any suggestions how to get Synfire to scan the VST3 plugin?