Sorry to bump a months-old thread, but I have exactly the same issue now, and the same conflict with NDATA plugin. (Only one google result when searching for that compiler error in the first post, and it's this thread!)
Unfortunately I'm actually using NDATA in my project, and need to find some way to make it co-exist with spine... Any ideas? Unity 5.1.3, and the latest spine runtimes as of today.