I just downloaded Couchbase 4.0 DP to give it a try on an older MacBook Pro, running MacOS 10.10.3. I previously had CB 3.0.3 running on that machine, and it ran fine.
As instructed, I deleted the previous files using:
rm -rf ~/Library/Application\ Support/Couchbase rm -rf ~/Library/Application\ Support/Membase
(Though there wasn’t a “Membase” directory on the machine.)
The application seems to launch correctly, with the icon appearing in the menu bar.
I then go to the web console and try to set up a new cluster. No matter what options I select, when I click the button the create the new cluster, the page switches to say “loading…” and never finishes, at least after 15-20 minutes. I tried different combinations of options, but every time the web console hangs. If I click “reload” the page goes back to the original splash screen with the “Setup” button. I tried restarting Couchbase, restarting the machine, and re-deleting the Application Support files, but nothing can get me past the setup stage.