Hi Dan,
I apologize for not having answered this before---we are overwhelmed by the new 1.8.0 releases.
This is a strange problem. Are you using an antivirus application? (I know this sounds weird, but some people are already using antivirus/firewall programs on Mac OS X). A few similar issues have been reported on Windows, and in all cases the problem was file corruption caused by antiviruses "protecting" file transfers.
Anyway, if you update to version 1.8.0 (I am about to start uploading installation packages for 1.8.0 RC3) you won't need a core application update. The current 1.8.0 version is fully stable.