http://lists.common-lisp.net/pipermail/slime-devel/2012-November/018677.html
The person here had a similar problem (but with SLIME). They discovered that the GEBEN package, which interfaces Emacs with DBGp protocol (which I use for debugging PHP scripts) was causing the problem. And sure enough, when I removed GEBEN then ENSIME launched successfully.
I'm not sure what is going on in the background, but any thoughts on how I can get these two packages to live together in peace?
Thanks for any help/suggestions.
Neil