I had the exact problem using the Eventide Update Utility 1.6.1 on OS X 10.8.2. Luckily, my wife isn't as concerned about updating her computers and I was able to run the utility on her MacBook running OS X 10.6 and the updater worked perfectly.
I contacted Eventide support and they confirmed that the EUU 1.6.1 doesn't yet run on Mountain Line. They're reportedly "working" on it.
